Whistleblower Rick Bright says the US lacks a plan to produce and fairly distribute a coronavirus vaccine when it becomes available.

The country could face “the darkest winter in modern history” unless leaders act decisively, he told a congressional panel on Thursday.

Mr Bright alleges he was ousted from a high-level scientific post after warning President Donald Trump’s administration to prepare for the pandemic.

“We don’t have (a vaccine plan) yet, and it is a significant concern, “Mr Bright said.

Asked if lawmakers should be worried, he responded, “absolutely.”

Mr Bright, a vaccine expert who led a bio-defence agency in the US Department of Health and Human Services, said the country needs a plan to establish a supply chain for producing tens of millions of doses of a vaccine, and then allocating and distributing them fairly.

Appearing before the House Energy and Commerce Committee, Mr Bright said one of his lowest moments came when his repeated efforts to jump-start US production of respirator masks went nowhere.

Rick Bright was director of the Biomedical Advanced Research and Development Authority. Photo: Getty

Mr Bright recalled getting emails in late January from Mike Bowen, an executive at a medical supply company called Prestige Ameritech, indicating that the N95 mask supply was “completely decimated”.

“He said, ‘We’re in deep s—, the world is. And we need to act,”‘ Mr Bright said.

“I pushed that forward to the highest levels I could in HHS and got no response. From that moment I knew that we were going to have a crisis for our health care workers because we were not taking action. We were already behind the ball.”

Republican lawmakers on the panel, for the most part, were careful not to attack Mr Bright directly.

But Representative Markwayne Mullins criticised Mr Bright for continuing to collect his $US285,000 ($A443,031) salary while first on sick leave for a spike in blood pressure and now on holiday as he tries to straighten out his work situation.

“You’re too sick to go into work, but you’re well enough to come here while getting paid,” said Mr Mullin. “I have a hard time understanding that.”

A federal watchdog agency has found “reasonable grounds” that Mr Bright was removed from his post as BARDA head after sounding the alarm at the Department of Health and Human Services.