The WHO experts have visited a number of high-profile sites linked to the pandemic origins.
The inspection of the Wuhan virology institute, which conducts research on the world's most risky diseases, will be one of the most-watched stops on the team's probe into the origins of the Covid-19 pandemic.
Members of the team have met with institute researchers and managers, experts, vendors, residents and media representatives, the spokesperson for China's National Health Commission, Mi Feng, told reporters at a briefing Thursday.
While he did not identify specific theories, Ben Embarek described some of them as irrational and insisted the investigators would not waste time chasing the wildest claims.
That appeared to reference allegations that the virus originated in bats and then spread to people in the city of Wuhan, where illnesses were first reported in late 2019.
Following two weeks in quarantine, the World Health Organization team that includes experts in veterinary medicine, virology, food safety and epidemiology from 10 nations has over the past six days visited hospitals, research institutes and a traditional wet market linked to numerous first cases.
The Wuhan Institute of Virology has been subject of several conspiracy theories that suggest a leak could have caused the city's first outbreak of COVID-19.
Scientists at the laboratory conduct research on some of the world's most risky diseases, including strains of bat coronaviruses similar to Covid-19.
The previous United States administration of President Donald Trump alleged that the coronavirus leaked from this Wuhan lab, citing its study of bat coronaviruses similar to the new coronavirus.
The US-secretary of state Mike Pompeo insisted previous year that there was "significant evidence" that the virus came from the lab, while releasing no proof and acknowledging that there was no certainty.
"I'm seeing a picture coming through of some of the scenarios looking more plausible than before", he said.
He also emphasised the World Health Organization investigators would "follow science and we follow facts" in reaching their conclusions.
"So that's also an important step that we were also able to understand where these stories are coming from". "We regret the misunderstanding".
The team visited the institute's P4 lab - Asia's first maximum-security lab equipped to handle Class 4 pathogens such as Ebola.
He said the team in Wuhan had been receiving new information about how the virus led to a pandemic, but did not elaborate.
Official statistics shows that there were at least 16 confirmed COVID-19 cases a year ago among almost 10,000 people living in the area when the coronavirus surfaced. "The work is moving ahead & we look forward to being able to talk about the results as soon as possible".