A US intelligence report has found no direct evidence that COVID started in China's Wuhan Institute of Virology. 

In a four-page report that was declassified on Friday, intelligence agencies said it was unable to discover the origins of the pandemic but said it could not rule out the possibility the virus came from a laboratory.

"The Central Intelligence Agency and another agency remain unable to determine the precise origin of the COVID-19 pandemic, as both (natural and lab) hypotheses rely on significant assumptions or face challenges with conflicting reporting," the report said.

The intelligence agencies did not find evidence of a specific incident at the Wuha Institute (WIV) that could have caused the outbreak despite "extensive work".

"We continue to have no indication that the WIV's pre-pandemic research holdings included SARSCoV-2 or a close progenitor, nor any direct evidence that a specific research-related incident occurred involving WIV personnel before the pandemic that could have caused the COVID pandemic."

Reports of several Wuhan lab researchers falling ill with respiratory symptoms in late 2019 are also inconclusive, the report argues, saying some of their symptoms weren't consistent with COVID.

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Four major US agencies believe the virus was transferred from animals to humans.

But two agencies - the Energy Department and the FBI - believe the virus leaked from a lab. The CIA and another agency have not made an assessment.

The report was issued after the US Congress passed a bill earlier this year giving US intelligence 90 days to declassify intelligence related to the Wuhan Institute of Virology.

Located in the city where the pandemic is believed to have started, the lab has faced intense scrutiny for its previous research into bat coronaviruses and reported security lapses.