The WHO investigators arrived in Wuhan, capital of Hubei province, last month to look for clues, and have visited hospitals that treated many of the earliest patients and a seafood market where cases of infection with the then-unknown virus first emerged in December 2019.
The team's visit to the Hubei Provincial Centre for Disease Control comes amid tight Chinese controls on access to information about the virus.
China has sought to avoid blame for alleged missteps in its early response to the outbreak, while promoting alternative theories that the virus originated elsewhere and may have been brought to Wuhan from outside the country.
The evidence the team assembles will add to what is expected to be a years-long quest for answers.
Pinning down an outbreak's animal reservoir requires massive amounts of research including animal samples, genetic analysis and epidemiological studies.
China has largely curbed domestic transmission through strict testing and contact tracing. Mask wearing in public is observed almost universally and lockdowns are routinely imposed on communities and even entire cities where cases are detected.
The most recent outbreaks have been mostly in the frigid northeast, with 33 new cases reported nationally on Monday across three provinces.
Despite that, China recorded more than 2000 new domestic cases of COVID-19 in January, the highest monthly total since the final phase of the initial outbreak in Wuhan last March. Two people died of the disease in January, the first reported COVID deaths in China in several months.
Schools have gone online and travel has been drastically cut during this month's Lunar New Year holiday, with the government offering incentives for people to stay put during the most important time for family gatherings across the vast nation.