The inspection of the Wuhan virology institute, which conducts research on the world's most dangerous diseases, will be one of the most-watched stops on the team's probe into the origins of the Covid-19 pandemic.
The sensitive mission, which China had delayed throughout the first year of the pandemic, has a remit to explore how the virus jumped from animal to human.
But questions remain over what the experts can hope to find after so much time has passed.
The convoy of cars drove past security to enter a virology institute shrouded in mist Wednesday morning, with the first car pausing briefly to take questions from journalists.
WHO team member Peter Daszak said the team was "looking forward to a very productive day and to asking all the questions that we know need to be asked".
Scientists think Covid-19 -- which first emerged in Wuhan and has gone on to kill more than two million people worldwide -- originated in bats and could have been transmitted to people via another mammal.
But there are no definitive answers so far.
There was speculation early in the pandemic that the virus could have accidentally leaked from the biosafety lab in Wuhan, although there was no evidence to back up that theory.