A World Health Organization-led team investigating the origins of the COVID-19 pandemic on Monday visited the Center for Disease Control and Prevention in China's central region of Hubei, where the outbreak emerged in late 2019.
The group of independent experts spent about 4-1/2 hours on its longest site visit since completing two weeks of quarantine on Thursday, and did not speak to waiting journalists.
But a WHO official in Geneva said that they had held "very good discussions" with their Chinese counterparts.
The WHO, which has sought to manage expectations for the mission, has said its members would be limited to visits organised by their Chinese hosts and have no contact with community members, because of health curbs.
The group has so far also visited hospitals where early cases were detected, markets, and an exhibition on the battle with the outbreak in the provincial capital of Wuhan.
"The visits that they have provide detailed information and all of this detailed information requires analysis which is ongoing between the international team and the Chinese counterparts. And all of that detailed analysis leads to more and more questions," Maria Van Kerkhove, WHO technical lead on COVID-19, told a Geneva news conference on Monday evening.
"Their focus is on the early cases they are having very good discussions around that."
Mike Ryan, WHO's top emergency official, said: "We continue to ask the questions, we continue to push for more data ... It's a detective story and you go through again and you answer more questions."
No full itinerary for the group's field work has been announced, and journalists covering the tightly controlled visit have been kept at a distance from team members.
Yanzhong Huang, senior fellow with the Council of Foreign Relations in Washington, said two weeks in the field was not much time for the experts.
"I don't think they have the time to get any conclusive results. It is more like communication and information exchange," Huang told Reuters by phone from Washington.
"It depends how diligent they are in digging new information but also about how cooperative and accommodating the Chinese side will be."
Beijing has sought to cast doubt on the notion that the coronavirus originated in China, pointing to imported frozen food as a conduit.
That hypothesis figured again on Sunday in the Global Times tabloid run by the ruling Communist Party's People's Daily.
On Sunday, the experts visited the Huanan seafood market linked to initial infections, and the Baishazhou wholesale food market, where a loudspeaker repeatedly announced that the sale of imported cold chain products was banned at the market.
(Interactive graphic tracking global spread of coronavirus: https://graphics.reuters.com/world-coronavirus-tracker-and-maps)
(Reporting by Martin Quin Pollard and Thomas Peter in Wuhan; Additional reporting by David Stanway in Shanghai and Stephanie Nebehay in Geneva; Writing by Tony Munroe; Editing by Gerry Doyle, Clarence Fernandez and Alison Williams)
