An international expert mission to Wuhan has concluded it was very likely that COVID-19 first passed to humans from a bat through an intermediary animal, while all but ruling out a laboratory leak.

The intermediate host hypothesis was deemed "likely to very likely", while the theory that the virus escaped from a lab was seen as "extremely unlikely", according to the long-awaited report.

The report from the international mission to Wuhan has been keenly anticipated ever since the expert team left China more than a month ago.

Delays in the publication of the findings, drafted in collaboration with the team's Chinese counterparts, had been blamed on coordination and translation issues, even as a diplomatic tug-of-war raged in the background over the report's contents.

During a lengthy press conference in Wuhan on Feb 9 at the end of the mission, the experts and their Chinese counterparts made clear that they could not yet draw any firm conclusions.

But they said they had worked to rank a number of hypotheses according to how likely they were.