Pick-up basketball games. Crowds gathering at an outdoor fish market. Family hikes along trails in Rock Creek Park. The warmer weather is bringing violations of social distance guidelines in the United States capital, even as health officials predict the city could become one of the next US hot spots in the coronavirus pandemic.

More than 1,200 people have tested positive for the virus, with 22 deaths, in Washington, DC. But national and local health officials predict that the worst is yet to come.

Last week, Mayor Muriel Bowser announced that models predict the virus may peak in the District of Columbia in May or June and may result in nearly one in seven Washington residents infected by the end of the year and a high-end death toll over 1,000.

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"We are concerned that the next wave … that DC could be in the second wave," Bowser said. "We want the message to get in everybody's head - that we see a level of infection in our city that if we aren't strict in our social distancing, the community spread will continue and we will have more people succumb to illness and perhaps death."

Dr Deborah Birx, coordinator of the White House coronavirus task force, has repeatedly mentioned the District of Columbia as a potential looming hot spot, along with Chicago, Detroit, Colorado and Pennsylvania. Birx said national health officials have "developing concerns" about the capital, noting that Washington, DC, appears to be in the early stages of a now-familiar pattern: a steady daily rise in reported infections that precedes a massive spike that overloads local health systems.

"We are concerned about the metro area of Washington and Baltimore," Birx to ABC's Good Morning America programme on Wednesday.

District of Columbia Mayor Muriel Bowser speaks about DC's coronavirus response in front of a table displaying hand sanitiser and personal protective equipment at a news conference [Patrick Semansky/AP Photo]

On Saturday, Birx said: "We're hoping and believing that if people mitigate strongly, the work that they did over the last two weeks will blunt that curve and they won't have the same upward slope and peak that New York, New Jersey, Connecticut and part of Rhode Island are having."

For most people, the new coronavirus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, or even death. The vast majority of people recover.

Washington DC's attempts to slow the spread through social distancing have been complicated by noncompliant residents. Last month, authorities were forced to essentially seal off the Tidal Basin around the Jefferson Memorial to keep crowds from gathering to view Washington's signature blooming cherry blossom trees.

A Washington, DC Metropolitan Police vehicle parked on the other side of police tape along the Tidal Basin to prevent people from visiting the cherry blossoms, a popular tourist attraction [Carolyn Kaster/AP Photo] [Daylife]

Over the weekend, as warm weather drew stir-crazy families outdoors, Bowser abruptly ordered a popular wharfside open-air fish market closed after photos on social media showed crowds gathering there.

"We had to close that market because the social distancing requirements were not being met," Bowser said Monday. "We cannot express enough that staying at home is every individual's responsibility to save lives."

Rock Creek Park, the massive 1,754-acre (710-hectare) green space at the heart of the capital, also drew healthy crowds of cyclists and hikers last weekend. For the most part, people seemed to be staying apart and sticking to their family clusters, with police officers on horseback patrolling the trails. But the physical reality of the hiking trails and bike paths made it impossible for everyone to stay 1.83 metres (6 feet) apart at all times.

Sounding genuinely fed up, Bowser, a Democrat, expressed frustration Monday with steady reports of pick-up basketball games and other gatherings still taking place.

"This is after we closed parks. This is after we put police tape around playground equipment. This is after we've taken down basketball hoops and tennis nets. We still have people gathering in places they know they shouldn't. We need the public's assistance here," Bowser said.

Stan Kiser helping set up portable fencing in the hope of forcing customers to practise social distancing at The Wharf's Fish Market, which was closed by DC officials over the weekend after large crowds gathered there [Andrew Harnik/AP Photo]

Violators of the city's stay-home order could face a 90-day jail sentence or a $5,000 fine. No one has been arrested or fined yet, and Bowser said she would rather not see police officers in that role.

"If we expect the police department to be able to make every single person do what they know they're supposed to do, we're going to be disappointed," she said.

DC Councilman Trayon White sounded equally frustrated. White said his daily rounds of his ward now include an unexpected new job: personally dispersing groups of people gathering on street corners.

"I'm telling people, 'It's a new day! Y'all can't stand up here. Right now, this is me, the councilmember, saying it. But in a minute, it's going to be police up here saying it. And I don't want that type of tension,'" White said. "We need officers to be addressing other issues."

White, a Democrat, said his current message to constituents is simple and stern.

"Go in the house, stay in the house, man," he said. "Stay out the way. Stay OUT THE WAY!"