An international expert mission to Wuhan in China has concluded that it was very likely that Covid first passed to humans from a bat through an intermediary animal, while all but ruling out a lab incident.

The experts said that the intermediary host hypothesis was deemed "likely to very likely", while the theory that the virus escaped from a laboratory was seen as "extremely unlikely".

This is according to the final version of the long-awaited report, of which AFP obtained a copy before the official release - due in the next few days.

Experts from the World Health Organization visited Wuhan in January and February to investigate the origins of the novel coronavirus.

The WHO's chief said that all hypotheses on the Covid-19 pandemic's origins remained open and needed further study, having read the report from international experts' mission to Wuhan.

"All hypotheses are open, from what I read from the report ... and warrant complete and further studies," director-general Tedros Adhanom Ghebreyesus told a virtual press conference from Geneva.

Read more: The origins of Covid-19

Last week, the former director of the US Centers for Disease Control and Prevention (CDC) said he believed the coronavirus that causes Covid-19 likely escaped from a lab in Wuhan.

"I still think the most likely etiology of this pathogen in Wuhan was from a laboratory, you know, escaped," Robert Redfield - who headed the CDC in the Trump administration - told CNN.

Also last week, the US said it expects the WHO investigation into the origins of the pandemic to require further study, perhaps including a return visit to China.

Marc Cassayre, charge d'affaires at the US mission to the UN in Geneva, also voiced hope that the Wuhan mission had access to the raw data and to the people required to make an independent assessment.

"We are hopeful that it will be based on science and be a real step forward for the world understanding the origins of the virus so we can better prepare for future pandemics," Mr Cassayre told a news briefing.

The probe was plagued by delays, concern over access and bickering between Beijing and Washington, which under former US President Donald Trump's administration accused China of hiding the extent of the initial outbreak.

Some team members have said China was reluctant to share vital data that could show the virus was circulating months earlier than first recognised in late 2019.

Team leader Ben Embarek said at a press briefing marking the end of the visit that the virus probably originated in bats, although it was not certain how it reached humans.

He also effectively ruled out a lab leak.

WHO director-general Tedros Adhanom Ghebreyesus later said that "all hypotheses remain open" and pledged full transparency.

Meanwhile, local media is reporting that more than 1.7 million residents in Wuhan have received a Covid-19 vaccine.

With no recorded cases of community transmissions since May 2020, life for residents is gradually returning to normal.