Experts from the World Health Organization met Chinese officials Friday ahead of their first site visits in Wuhan for a coronavirus origins probe which will take in a food market presumed to be "ground zero" of the pandemic.

The fieldwork was set to begin in earnest in the afternoon, after being hobbled by delays -- and amid fears over access and the strength of evidence a year after the virus emerged.

The team will visit hospitals, as well as meeting scientists, first responders and some of the early patients to be hit by the then-unknown coronavirus that has gone on to kill more than two million people across the world and flatline the global economy.

Crucially, "field visits will include the Wuhan Institute of Virology, Huanan market, Wuhan CDC laboratory", the WHO said in a tweet late Thursday -- three sites now indelibly linked with the virus.

The Huanan market, which remains boarded up, is believed to have been the outbreak's first major cluster.

Meanwhile, the Wuhan Institute of Virology houses a virus testing facility which was weaponised by former US president Donald Trump, who until his final days in office pushed the unsubstantiated theory that the virus escaped from there.

The mission's exact itinerary remains unclear -- tweets from the WHO and their experts are so far the main source of information.

The highly politicised mission has been beset by delays with China refusing access until mid-January, while Washington has demanded a "robust and clear" investigation.

China on Thursday warned the US against "political interference" during a trip which the WHO insists will be tethered tightly to the science behind how the virus jumped to humans.

Beijing is desperate to take the air out of the blame game and instead train attention on its handling and recovery from the outbreak.

In a tweet late Thursday, WHO chief Tedros Adhanom Ghebreyesus said he had had a "frank discussion" with China's Health Minister Ma Xiaowei.

"I asked that the international scientists get the support, access & data needed, and the chance to engage fully with their Chinese counterparts," he said.

The experts left a two-week quarantine on Thursday under the glare of the global media.

China's National Health Commission says 4,636 people have died in the country as a result of the virus.

The nation's GDP grew 2.3 percent in 2020, the only major economy to do so.

In comparison, more than 400,000 Americans have died so far as the sickness rips through its population and economy, while the UK recorded its 100,000th fatality this week.