Transmission from animals was likely but so far "the reservoir hosts remain to be identified,'' said Liang Wannian, head of the China team, at a press conference.

Liang also said the virus could have been circulating in other regions before it was identified in Wuhan at the end of 2019. He said that there had been no substantial spread of the virus in the city before the late 2019 outbreak.

The WHO joint team includes 17 Chinese experts and 17 international experts from 10 countries.