Donald Trump has said he isn’t concerned at all about the coronavirus getting closer to the White House after it was revealed that an attendee at grassroots conservative conference CPAC had tested positive.

On a day when it also emerged that the nation’s capital had recorded its first case, the American Conservative Union said on Saturday that a participant at CPAC, which was attended by both Trump and the US vice-president, Mike Pence, had tested positive for coronavirus.

The White House said there was no indication that either Trump or Pence had been close to the infected attendee.

Asked if he was concerned about the virus getting closer, Trump said: “No, I’m not concerned at all. No, I’m not. We’ve done a great job.”

When asked whether his thousand-person campaign rallies would would continue in light of the CPAC case, the president replied: “We’ll have tremendous rallies.”

Trump held his most recent campaign rally last Monday in Charlotte, North Carolina. He waved off other questions to join a dinner for the president of Brazil, who was visiting Trump at the president’s home in south Florida.

Saturday also marked the first case in the District of Columbia, with mayor Muriel Bowser saying testing at the public health lab of the DC Department of Forensic Sciences yielded its first presumptive positive.

The American Conservative Union put out a statement on Twitter on Saturday evening that said a CPAC attendee “has unfortunately tested positive” and noted that their “exposure” occurred before the conference.

The gathering took place in Oxon Hill, Maryland, in late February and was attended by many leading party figures as well as thousands of grassroots members, often accompanied by spouses, children and friends.

“A New Jersey hospital tested the person and the CDC [the federal public health agency the Centers for Disease Control and Prevention] confirmed the result. The individual is under the care of medical professionals in New Jersey and has been quarantined,” the statement continued.

It informed anyone with concerns to contact the ACU or the department of health of the state of Maryland and urged people to remain calm.

The statement said: “This attendee had no contact with the president or vice-president and never attended the events in the main hall.”

It noted that the Trump administration had been informed of the situation.

“We will continue regular communication with all appropriate government officials,” the statement continued.

The ACU chairman, Matt Schlapp, had previously tweeted a proud message about introducing the president at the CPAC event last weekend.

He then retweeted several posts from a journalist at the conservative-leaning RealClearPolitics media outlet.

The governor of Maryland, Larry Hogan, said the state had acted as soon as it became aware of the positive test.

“Immediately after learning of this individual’s interactions in our state, we began coordinating with the White House, the CDC and federal officials, the New Jersey Department of Health, Prince George’s County officials, and conference organizers,” Hogan said.

“Due to the scale of this conference, we are urging attendees who are experiencing flu-like symptoms to immediately reach out to their health care provider. We are providing this update not to unnecessarily raise alarm, but in the interest of full transparency and out of an abundance of caution.”

Also on Saturday, a marine at Virginia’s Fort Belvoir became the first military case of coronavirus reported inside the US.

The marine was being treated at Fort Belvoir Community Hospital, located south of Washington, and had recently returned from an overseas assignment, Pentagon spokesman Jonathan Hoffman said on Twitter.

The Italian government is to lockdown the northern region of Lombardy, as it battles to contain the spread of the coronavirus. A draft decree would extend the quarantined areas, so-called “red-zones”, ordering people not to enter or leave the region.

The country is grappling to contain Europe’s worst outbreak of Covid-19, which has claimed 233 lives and infected a total of 5,883 people.

Italian authorities announced that a new decree containing draconian measures would be approved later on Saturday. It will include the power to impose fines on anyone caught entering or leaving Lombardy, the worst-affected region, until 3 April. People may be allowed in and out for serious reasons. The decree provides for banning all public events, closing cinemas, theatres, gyms, discos and pubs. Religious ceremonies such as funerals and weddings will also be banned.

Rome is also considering prolonging the closure of schools across the country until 3 April, while major sporting events, such as Serie A football games, will be played behind closed doors.

The number of coronavirus cases in Italy leapt by more than 1,200 in a 24-hour period, the civil protection agency said on Saturday. It is the biggest daily rise since the outbreak began two weeks ago.

The number of cases in the country rose to 5,883 on Saturday from 4,636 announced on Friday, with the spread showing little sign of slowing. In total there are now 5,061 cases, not including those who have died or recovered.

The northern regions of Lombardy, Emilia-Romagna and Veneto are the hardest hit, representing 85% of cases and 92% of recorded deaths.

“We will win this battle if our citizens adopt a responsible attitude and change their way of living,” the head of Italy’s civil protection agency, Angelo Borrelli, told a press conference.

The outbreak is severely damaging the Italian economy, with warnings that the tourism sector alone could experience €7.4bn (£6.4bn) of losses during this trimester.

The state of Florida has reported two deaths from coronavirus, the first US fatalities outside the west coast, as thousands remain quarantined on a cruise ship moored off the coast of California, near San Francisco.

Health officials said the deaths in Florida involved two people in their 70s who had travelled overseas, one in Santa Rosa County and the other near Fort Myers. The US death toll is now 17, with 333 confirmed cases in the Covid-19 novel coronavirus outbreak.

And on the Grand Princess cruise ship moored outside San Francisco, nearly half of the 46 people tested for coronavirus onboard have returned a positive result, vice president Mike Pence said. The fate of its more than 3,500 passengers and crew from more than 50 countries remains unclear.

Pence said 21 positive results had been recorded – 19 crew members and two passengers – and that “those that will need to be quarantined will be quarantined. Those who will require medical help will receive it.” He urged elderly Americans to consider carefully taking future cruises during the crisis.

There is little detail as to where quarantined and sick passengers will be taken. Previously, military sites have been used to quarantine holidaymakers from the Diamond Princess, moored off Yokohama. On the Grand Princess, some passengers have already complained about the handling of the situation, saying they learned of the coronavirus cases from media reports, and there are concerns for one passenger who has stage 4 cancer.

There are 2,422 guests and 1,111 crew on the vessel, with more than 140 Britons and four Australians among them.

Globally, the virus has now killed nearly 3,500 people and infected more than 100,000 across 92 nations and territories. Italy and Iran have become the latest hotspots with sharp rises in confirmed cases, recording 4,636 and 4,747 respectively.

In China, 99 new cases were confirmed, and 29 deaths as of midnight Friday. In official data released on Saturday, China’s exports fell 17.2%, the biggest drop since February 2019 during the trade war with the US, and imports dropped 4%.

The US government plans to take the Grand Princess to a “non-commercial port” where all the passengers and crew would be tested, however, President Donald Trump said on Friday he would prefer not to allow the passengers onto American soil.

“I like the numbers being where they are,” said Trump, who appeared to be explicitly acknowledging his political concerns about the outbreak: “I don’t need to have the numbers double because of one ship that wasn’t our fault.”

Closer to the epicentre of the global outbreak, Hong Kong further sealed itself off from the outside world, with authorities advising Hongkongers against all non-essential travel abroad, and making all arrivals complete a health declaration form.

Previously, the measure, which will come into force from Sunday, was required only for mainland Chinese passengers. The city has reported 106 cases and two deaths in the past six weeks, according to its health officials.

In Australia, authorities are working to trace about 70 patients of a doctor who continued to see patients despite falling ill with coronavirus-like symptoms. He fell ill in the US during a flight from Denver to San Francisco on 27 February before flying back to Melbourne and working throughout the following week. He was later confirmed to have the virus and Toorak clinic, where he works, has since been closed.

Victoria’s health minister, Jenny Mikakos, said: “I have to say I am flabbergasted that a doctor that has flu-like symptoms has presented to work,” Mikakos said.

Equally astonished were police in Sydney, who appealed for calm after a brawl broke out between three women in a supermarket over toilet paper amid continued panic buying. “We just ask that people don’t panic like this when they go out shopping,” said acting inspector Andrew New from New South Wales police. “There is no need for it. It isn’t the Thunderdome, it isn’t Mad Max, we don’t need to do that.

“There is no need for people to go out and panic buy at supermarkets, paracetamol and canned food or toilet paper.”

In the meantime, passengers aboard the Grand Princess remained holed up in their rooms as they awaited word about the fate of the ship. Some said ship officials only informed them of the confirmed coronavirus cases after they first learned about it from news reports.

Passenger Kari Kolstoe, a retiree from North Dakota has stage-4 cancer and is particularly concerned. Kolstoe, 60, said she and her husband, Paul, 61, had looked forward to the cruise to Hawaii as a brief, badly needed respite from the grind of medical intervention she has endured for the past 18 months.

Now facing the prospect of a two-week quarantine far from home in Grand Forks, she worried their getaway cruise will end up causing a fateful delay in her next round of chemotherapy, scheduled to begin early next week.

“It’s very unsettling,” she said in a telephpone interview from the ship on Friday. “It’s still a worry that I’m going to not get back.”

Besides the implications for cancer treatment is the fear of falling ill from exposure to a respiratory virus especially dangerous to older people with chronic health conditions and suppressed immunity. “I’m very at risk for this,” said Kolstoe, whose rare form of neuroendocrine cancer has spread throughout her body. “Me staying on here for a lot of reasons isn’t good.”

Steven Smith and his wife, Michele, of Paradise, California, went on the cruise to celebrate their wedding anniversary. They said they were a bit worried but felt safe in their room, which they had left just once since Thursday to video chat with their children. Crew members wearing masks and gloves delivered trays with their food in covered plates and left them outside their door.

To pass the time they have been watching television, reading and looking out the window, they said. “Thank God, we have a window!” Steven said.

An epidemiologist who studies the spread of virus particles said the recirculated air from a cruise ship’s ventilation system, plus the close quarters and communal settings, made passengers and crew vulnerable to infectious diseases. “They’re not designed as quarantine facilities, to put it mildly,” said Don Milton of the University of Maryland. “You’re going to amplify the infection by keeping people on the boat.”

Another Princess ship, the Diamond Princess, was quarantined for two weeks in Yokohama, Japan, last month because of the virus. Ultimately, about 700 of the 3,700 people aboard became infected in what experts pronounced a public-health failure, with the vessel essentially becoming a floating germ factory.

In the US, officials in Austin cancelled this year’s SXSW festival, a major tech and music conference, amid coronavirus concerns. SXSW, which draws 400,000 visitors, was scheduled for 13 to 22 March.

Austin’s mayor, Steve Adler, said: “I’ve gone ahead and declared a local disaster in the city and associated with that, have issued an order that effectively cancels SXSW.”