American healthcare systems could be overwhelmed by a need for hospital beds and breathing machines in intensive care units under a growing coronavirus threat.

US health officials suggest that a surge in demand for inpatient care could impact 200,000 to as many as 2.9 million patients, though there are fewer than 100,000 intensive care unit beds available, according to the American Hospital Association, and other reports estimate there are as few as 45,000.

The US Department of Health and Human Services reported that an estimated 64,000 people will also need medical ventilation amid a mild Covid-19 outbreak, but the country's hospital systems have only "about 62,000 full-featured ventilators on hand and an additional 8,900 in the national stockpile".

In the event of a confirmed pandemic, the department has estimated that 865,000 Americans would be hospitalised during a "moderate" outbreak or as many as 9.9 million in a "severe" pandemic.

More than 20 people have died in the US following infections of the flu-like respiratory illness, which has sickened thousands in more than a dozen countries, sending US markets into a tailspin amid fears of a pandemic that has gripped economies and strained communities and health systems worldwide as millions of people face quarantine.

American hospitals are beginning to adjust their guidelines to respond to the outbreak - from limiting the use of gowns and masks and outsourcing patient services to off site clinics - following a dramatic spike in infections last week.

Whether there will be enough ventilators or other equipment to treat coronavirus patients, public health agencies also warn there may not be enough staff to operate them, as hospitals become overrun with patients and combat the transmission of the virus from health workers to otherwise healthy people.

Currently, "US hospitals routinely operate at or near full capacity and have limited ability to rapidly increase services," according to John Hopkins Center for Health Security. "There are currently shortages of healthcare workers of all kinds. Emergency departments are overcrowded and often have to divert patients to other hospitals."

Dan Diekema, director of infectious disease at the University of Iowa Medical Center, said that an "overwhelmed" system means "bringing it to a breaking point where dire decisions have to be made, such as rationing ventilators and/or being unable to provide supportive care for some critically ill patients due to lack of capacity," according to the Huffington Post.

Questioning whether the US is prepared for an outbreak at this scale, Dr Bruce Aylward with the World Health Organisation compared China's war-like mobilisation to combat the virus to the cost of care and limited resources in the US as a "barrier to speed" in controlling the outbreak.

He told The New York Times: "That'll kill you. That's what could wreak havoc. This is where universal health care coverage and security intersect. The US has to think this through."

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Last week, Donald Trump signed an $8.3bn emergency funding measure passed by Congress to help state and local efforts to combat the virus.