Top US scientist Anthony Fauci has urged China to release the medical records of nine people who fell sick with a coronavirus-like illness prior to the outbreak, saying they could provide insights into whether the pandemic came from a lab.

The "lab leak" theory has gained increasing traction, fueled by reports that six miners fell ill in 2012 and three researchers from the Wuhan Institute of Virology became sick in 2019 after visiting a bat cave in the southwestern Chinese province of Yunnan.

In an interview with The Financial Times on Thursday, US President Joe Biden's chief medical advisor said the records could answer critical questions over the contested origins of Covid-19 in Wuhan, where a pandemic that has killed over 3.6 million people worldwide began.

"I would like to see the medical records of the three people who are reported to have got sick in 2019," Fauci said. "Did they really get sick, and if so, what did they get sick with?

"The same with the miners who got ill years ago... What do the medical records of those people say?" he asked.

"It is entirely conceivable that the origins of Sars-Cov-2 was in that cave and either started spreading naturally or went through the lab."

Fauci has previously said he believes Covid-19 was a natural occurrence, though he has admitted to not being "100 percent" certain.

The Wuhan Institute of Virology is at the center of theories that Covid-19 leaked from a lab
The Wuhan Institute of Virology is at the center of theories that Covid-19 leaked from a lab AFP / HECTOR RETAMAL

China wholly rejects the lab leak theory, and has instead accused the US of peddling conspiracies and politicising the pandemic to divert attention from the high death rates there. Evidence to support the hypothesis is also scant.

The natural origin theory -- backed as the most likely by a WHO expert team who visited China last year -- holds that the virus emerged in bats then passed to humans, likely via an intermediary species.

Beijing's foreign ministry Friday cited the findings of that visit in dismissing Fauci's comments -- and cited unsubstantiated claims that the virus first appeared at a US biological research center at Fort Detrick.

It pointed to a Wuhan Institute of Virology statement from March when asked if Beijing would share the medical records.

"We hope that people who do not hold conspiracy theories, who do respect the facts and who do respect the truth can get factual answers from this statement," Wang Wenbin, a spokesman for the Ministry of Foreign Affairs, told a briefing.

A widely accepted theory at the start of the pandemic, scientists have yet to find a virus in either bats or another animal that matches the genetic signature of SARS-CoV-2.

Biden last week ordered US intelligence agencies to report to him in the next three months on whether the Covid-19 virus first emerged in China from an animal source or from a laboratory accident.

Coronavirus