The World Health Organization investigators in Wuhan say they have been given data 'no-one has seen before' and have not ruled out that Covid escaped from a lab.
More than a year after China revealed the disease, the UN agency accused of parroting Beijing's false claims was allowed to visit the infamous Institute of Virology on Wednesday.
The Communist Party is supposed to have granted them scope to explore how Covid-19 jumped from animal to human - but there are grave doubts over what they will be able to uncover.
Dr Peter Daszak, a British zoologist on the WHO team, told Sky News last night: 'They are sharing data with us that we have not seen before - that no one has seen before.
'They are talking with us openly about every possible pathway. We really are getting somewhere and I think every member of the team would say that.'
Dr Daszak and his colleagues were seen driving into the infamous laboratory shrouded in mist this morning.
He told reporters the team was 'looking forward to a very productive day and to asking all the questions that we know need to be asked'.
Most scientists believe Covid - which has killed more than two million people worldwide - originated in bats and could have been transmitted to people via another mammal.
In Washington, the Trump administration repeatedly demanded that the laboratory should be probed and last month then-secretary of state Mike Pompeo released new intelligence about the facility.
Among the dossiers, were claims that researchers at the lab fell ill in the fall of 2019 with symptoms consistent with Covid-19, that scientists there were working with a bat coronavirus that is 96.2 percent similar genetically to the virus that causes Covid, and that the lab has secret links to the Chinese military.
Experts have repeatedly dismissed the idea that the virus was manufactured, and Mr Pompeo did not suggest that Covid was intentionally engineered or released on purpose.
Instead, he raised the possibility that it was a natural virus that had accidentally escaped from the lab through sloppy safety protocols.
'Accidental infections in labs have caused several previous virus outbreaks in China and elsewhere, including a 2004 SARS outbreak in Beijing that infected nine people, killing one,' the State Department said in a briefing document.
The most shocking revelation in Pompeo's release was intelligence suggesting that workers at the Wuhan lab fell ill with 'symptoms consistent with both COVID-19 and common seasonal illnesses' in the fall of 2019, months before the wider outbreak in Wuhan.
The WHO experts stayed inside the institute for nearly four hours on Wednesday, before driving away without stopping to talk to media waiting outside.
Police in black uniforms and face masks lined the road to separate the crowds of reporters from the cars.
According to the state-run Global Times, the team also visited the P4 lab - Asia's first maximum-security lab equipped to handle Class 4 pathogens (P4) such as Ebola.
There was speculation early in the pandemic that the virus could have accidentally leaked from the biosafety lab in Wuhan, although there was little evidence to back up that theory.
China has faced criticism at home and abroad for covering up the initial outbreak and concealing information when it first emerged in Wuhan in December 2019.
But Dr Daszak told journalists on Tuesday the mission was proceeding 'very well', as the group was driven into an animal disease control centre.
He said they had visited the Huanan seafood market, where the fist cases of coronavirus emerged, and that they were 'seeing new information and it's good, it's very valuable stuff.'
Dr Daszak told Sky: 'We are in the market looking around on our own and asking questions, we are meeting with market managers, with vendors who worked there and people from the community and asking them questions.
'We are talking to people who collected samples from the floor of the market that then tested positive. That's the sort of information we are getting with the person that really matters.'
China is also determined to put the focus on its recovery from the outbreak, and the WHO team toured a propaganda exhibition celebrating China's recovery from the pandemic in Wuhan on Saturday.
On Sunday the team went to the market where one of the first reported clusters of infections emerged over a year ago, which Daszak tweeted was a 'critical' stop.
Other stops include the hospital which treated some of the first coronavirus cases.
Shi Zhengli, one of China's leading experts on bat coronaviruses and deputy director of the Wuhan lab, raised some eyebrows in a June 2020 interview with Scientific American magazine in which she said she was initially anxious over whether the virus had leaked from the facility.
But subsequent checks revealed that none of the gene sequences matched the viruses held by the lab, Shi said, adding: 'I had not slept a wink for days.'
She later said she would 'bet her life that (the new coronavirus) had nothing to do with the lab', according to Chinese state media.
This article has been adapted from its original source.
