The United States has surpassed China and Italy as the country with the most coronavirus cases, as New York, New Orleans and other hot spots faced a surge in hospitalisations and looming shortages in supplies, staff and sick beds.
Medical facilities were running low on ventilators and protective masks and were hampered by limited diagnostic testing capacity.
The number of US cases of coronavirus reached 81,378. China was second with 81,285 cases, and Italy third with 80,539 cases.
At least 1,178 people in the United States have died from COVID-19, according to a running tally based on reports from state and local public health authorities.
An expected shortfall of ventilators - machines that support respiration for people who have lost the ability to breathe on their own - was substantial, as a surge of cases overwhelms New York hospitals, New York Governor Andrew Cuomo told a news conference.
"Any scenario that is realistic will overwhelm the capacity of the healthcare system," he said. "The number of ventilators we need is so astronomical - it's not like they have them sitting in the warehouse," Cuomo added. "There is no stockpile available."
At least one New York hospital has begun a trial of sharing single ventilators between two patients.
Dr. Craig Smith, surgeon in chief at New York-Presbyterian/Columbia University Medical Centre in Manhattan, wrote to staff that teams had worked "day and night" to get the split-ventilation experiment going.
Louisiana could be the next US epicentre. In New Orleans, the state's biggest city, Mardi Gras celebrations last month were believed to have fuelled the outbreak.
Louisiana Governor John Bel Edwards warned that his state, reporting about 1,800 infections, including at least 83 deaths is rapidly running out of beds and ventilators.
In New York state, the goal is to make as many as 140,000 hospital beds available, up from the current capacity of 53,000, and authorities are scouting new sites, Cuomo said.
The projected ventilator shortfall and surge in hospitalisations has already raised the prospect of rationing healthcare.
Asked about guidelines being drafted on how to allocate ventilators to patients in case of a shortage, New Jersey Governor Phil Murphy said such bioethical discussions "haunted him" but were unavoidable in the current situation.
"We have to hope for the best, but plan for the worst," Murphy told a news conference.
Outside New York and New Orleans, other hot spots appeared to be emerging around the country, including Houston and Detroit.
Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, told a public radio station that the changing weather could help fight the virus because generally warm and moist conditions are better than a cold, dry winter.
"We hope we get a respite as we get into April, May and June. It is likely to come around next season because it's a very vigorous virus," Fauci said.
Australian Associated Press