The World Health Organisation (WHO) mission to Wuhan may be a "hallmark moment" as the global community seeks to find answers to where the coronavirus came from, but expectations should be tempered, say experts.

"We should see this effort as very much the beginning of the investigation," said Professor Dale Fisher, an infectious disease expert from the National University Hospital in Singapore who was part of the WHO technical mission to China in February last year.

Since last week, the international team of experts has visited the Huanan seafood market where the earliest outbreak was documented, another wet market, two hospitals that treated Covid-19 patients as well as a cold-chain storage facility.

It is slated to visit the Wuhan Institute of Virology, which has a bank of genetic sequences of bat coronaviruses going back to the 2003 Sars epidemic.

Evidence suggests the Covid-19 virus originated in horseshoe bats, although scientists have yet to ascertain if it was transmitted directly to humans or through an intermediate host.

"They will also analyse a lot of data from contact tracing efforts, results of animal swabs, genome sequencing, etc. It's very unlikely that conclusions will be reached on this occasion. They are more likely to develop hypotheses and define what further results and future work" are needed, said Prof Fisher.

Even as the WHO mission began its investigation after a two-week quarantine, Chinese state media have continued to cast doubts over whether the virus started in the central Chinese city more than a year ago. Latching on to the international team's visit to the cold-chain storage facility on Sunday, state media Global Times claimed Chinese netizens had again questioned if it was possible that the virus came into Wuhan through cold-chain products.

At the height of a backlash last year, Beijing pushed a hypothesis that the virus may not have originated in Wuhan, but was imported into the country.

"The best outcome will be achieved if the world allows a scientific investigation in a 'no blame' environment. Political threats are very detrimental. In any outbreak investigation, we know that outcomes are hampered if the 'no blame' philosophy is not core," said Prof Fisher.

The WHO mission is subjected to tight controls by the Chinese authorities, who decide how much access the team gets.

Earlier last month, WHO chief Tedros Adhanom Ghebreyesus criticised Beijing for delaying the expert team's visit.

"Illuminating the origins of the pandemic would be of obvious value for structural changes that might help prevent the next pandemic, or at least identify it sooner, though we need to be careful of over-preparing for one particular pandemic scenario when the next pathogen may be fundamentally different in its transmissibility and severity," said Associate Professor Alex Cook of the Saw Swee Hock School of Public Health.

"However, it's been over a year since the pandemic first emerged in late 2019, so hope for important findings beyond what is already known should be tempered."

There are scant details about the mission's itinerary, but team member Peter Daszak, an expert on disease ecology, tweeted yesterday that the group met key staff responsible for livestock surveillance in Hubei province.

The head of the WHO's emergencies programme, Dr Michael Ryan, on Monday also put a lid on expectations that the probe will uncover answers to all the questions about Covid-19's origins, saying the fact-finding mission was part of a "detective story".

First documented in Wuhan in late 2019, the virus has spread around the world and killed more than two million people.

Calls for an independent probe into the origins of the virus were initially met with anger by China, but President Xi Jinping eventually agreed after more than 100 countries backed a resolution for such an inquiry.

"In my view, far more important than a mission to investigate the origins would be a critical review of how so many governments bungled their response once Covid-19 was already known about, and whether the WHO's processes from the point it was first notified of the disease to subsequently declaring it capable of human to human transmission, to be a public health emergency of international concern, and finally calling it a pandemic, could have been improved," said Prof Cook.