On Thursday, the team completed two weeks of quarantine following its arrival in China, moving to a lakeside hotel in the central Chinese city where the deadly virus emerged in late 2019.
The group is expected to spend two more weeks in China, and will visit the seafood market at the centre of the early outbreak. It will also visit the Wuhan Institute of Virology. One hypothesis, rejected by China, is that the outbreak was caused by a leak at the government lab.
The mission has been plagued by delays, concern over access and bickering between China and the United States, which has accused China of hiding the extent of the initial outbreak and criticised the terms of the visit, under which Chinese experts conducted the first phase of research.
"It is important to remember that the success of this mission and origin-tracing is 100% depending on access to the relevant sources," Thea Fischer, a Danish member of the team, told Reuters on Thursday.
"No matter how competent we are, how hard we work and how many stones we try to turn, this can only be possible with the support from China," she said.
The origin of COVID-19 has been highly politicised.
The investigating team had been set to arrive in Wuhan earlier in January, and China's delay of their visit drew rare public criticism from the head of the WHO, which former U.S. President Donald Trump accused of being "China-centric".
China has pushed the idea that the virus existed abroad before it was discovered in Wuhan, with state media citing the presence of the virus on imported frozen food packaging and scientific papers saying it had been circulating in Europe in 2019.
China's foreign ministry has also hinted that the sudden closure of a U.S. army laboratory at Fort Detrick in Maryland in July 2019 was linked to the pandemic.
"At the early stage in China, it was a burden particularly for Wuhan people when everyone was calling it a Wuhan virus, which was humiliating," said Yang You, a 30-year-old Wuhan resident. "If it could be traced to the source clearly, in my opinion, it could clear either China's or Wuhan's name."
