China has long said the lab, the Wuhan Institute of Virology, never possessed the COVID-19 virus.

But Tedros told a briefing in Genevaon Saturday (AEDT): “Some questions have been raised as to whether some hypotheses have been discarded. Having spoken with some members of the team, I wish to confirm that all hypotheses remain open and require further analysis and study.”

“Some of that work may lie outside the remit and scope of this mission. We have always said that this mission would not find all the answers, but it has added important information that takes us closer to understanding the origins of the COVID-19 virus,” he said.

Tedros said a summary report of the mission’s findings could be ready as early as next week, followed by a final report “in the coming weeks”. Both would be made public.

The mission has said its main hypotheses are that the virus originated in a bat, although there are several possible scenarios for how it passed to humans, possibly first by infecting another species of animal.

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It followed months of negotiation with Beijing. Stung by criticism that it initially covered up the extent of the crisis, Chinese state media and officials have promoted the theory that the virus didn’t start in China, but was brought in. Among the promoted origin theories were imported frozen-food packaging, international travellers and even a US cycling team competing in China.

When pressed on why the mission did not believe a lab could have been the source, Embarek said lab scientists had told his team they didn’t have it. If they had been studying it before the outbreak, he said, it would not have been a secret.

“Usually laboratory researchers who work and discover new viruses would immediately publish their findings. That’s a common practice around the world, particularly with new, interesting viruses,” he said.