China refused to give raw data on early COVID-19 cases to a World Health Organization-led team probing the origins of the pandemic, one of the team's investigators said, potentially complicating efforts to understand how the outbreak began.

The team had requested raw patient data on 174 cases that China had identified from the early phase of the outbreak in the city of Wuhan in December 2019, as well as other cases, but were only provided with a summary, said Dominic Dwyer, an Australian infectious diseases expert who is a member of the team.

Such raw data is known as "line listings", he said, and would typically be anonymised but contain details such as what questions were asked of individual patients, their responses and how their responses were analysed.

"That's standard practice for an outbreak investigation," he told Reuters on Saturday via video call from Sydney, where he is currently undergoing quarantine.

He said that gaining access to the raw data was especially important since only half of the 174 cases had exposure to the Huanan market, the now-shuttered wholesale seafood centre in Wuhan where the virus was initially detected.