Emergency field hospitals were readied in New York's Central Park and at the home of the US Open tennis tournament as the number of American deaths from the coronavirus pandemic surged past 4,000 — higher than the toll in China.

The pandemic has killed more than 1,700 New Yorkers and President Donald Trump, a native of the city, warned in Washington of “a very, very painful two weeks” to come for the entire country.

Already the hardest-hit area, America's financial capital is in a race to ramp up hospital capacity before cases peak.

Around a dozen tents, equipped with 68 beds and 10 ventilators, have been put up in Manhattan's iconic park, with Covid-19 patients expected to start arriving.

“You see movies like 'Contagion' and you think it's so far from the truth, it will never happen. So to see it actually happening here is very surreal,” 57-year-old passerby Joanne Dunbar told AFP on Tuesday.

Declared coronavirus cases across the US surged to 189,510 early on Wednesday, according to a running tally by Johns Hopkins University, with 4,076 deaths.

That is more than the 3,310 fatalities reported by China.

New York state has seen far more cases — 76,000 — and deaths than any other since announcing its first infection on March 1 and quickly emerging as the epicentre of the US outbreak.

Mayor Bill de Blasio said on Tuesday the city was tripling hospital capacity in a bid to get ready for the peak of the pandemic expected in two to three weeks.

“[We] will require a level of hospital capacity we've never seen [...] never even conceived of,” he told NBC.

Plea to evacuate

Fallout is spreading wider every day across the world's biggest economy.

The captain of the nuclear powered aircraft carrier Theodore Roosevelt, one of the most fearsome assets in the US arsenal, pleaded for large-scale evacuation, saying that the virus was spreading uncontrollably through his crew, currently in the US Pacific territory of Guam.

“We are not at war. Sailors do not need to die,” Captain Brett Crozier wrote in a letter to his superiors, US media reported.

Defense Secretary Mark Esper later downplayed the drama, saying that no one was “seriously ill".

But in New York, officials are already in full blown crisis management mode, scrambling to deal with the influx of sick when hospitals are already overwhelmed and medical supplies strained.

South of Central Park, the Javits Convention Centre is now operational with nearly 3,000 beds after it was adapted by the Army Corps of Engineers.

It will take non-coronavirus patients to ease the burden on hospitals focusing on the virus.

A few blocks away at Pier 90 sits the white, imposing US navy hospital ship Comfort, with 1,000 beds and 12 operating rooms — also for non-coronavirus patients.

A 350-bed facility at the Billie Jean King National Tennis Centre in Flushing Meadows-Corona Park, where the US Open tennis takes place every summer, is due to start receiving coronavirus patients next week.

Governor Andrew Cuomo — whose brother, CNN anchor Chris Cuomo, announced on Tuesday that he had the virus — warned New Yorkers that the fight to defeat Covid-19 was going to be a long one.

“Calibrate yourself and your expectations so you're not disappointed every day you get up,” he told reporters.

'Sneeze shields'

Tim Mosher — nurse team leader at the Samaritan's Purse field hospital in Central Park — said the site's 70 staff, mostly volunteers, would stay for as long as needed.

Mosher, more used to operating in disaster zones after spells treating Ebola victims in Liberia and Cholera patients in Haiti, said it was “sad” they were in New York.

“But we want it to be hopeful also that it sends a signal to the city that we care, [and] we're here,” the 58-year-old told AFP.

New York's normally teeming streets are almost empty, while masked faces are a common sight among the few people that can be seen, including cleaning crews working harder than ever.

At D'Agostino supermarket on First Avenue, manager Larry Grossman has installed glass partitions to protect cashiers from ill customers and put up signs about social distancing.

“[Still] we have a lot of people getting sick, a lot of people refusing to work,” he told AFP.

The Dow suffered its biggest quarterly loss since 1987 and former US president Barack Obama chastised those who “denied warnings” of a pandemic, in a thinly veiled swipe at his successor Trump