Hui Ka Yan, the billionaire chairman of beleaguered property developer China Evergrande Group, has been placed under police control, according to people with knowledge of the matter.

Hui was taken away by Chinese police earlier this month and is being monitored at a designated location, the people said, asking not to be identified because the matter is private.

It’s not clear why Hui is under so-called residential surveillance, a type of police action that falls short of formal detention or arrest and doesn’t mean Hui will be charged with a crime. Still, the measure means he is unable to leave the location, meet or communicate with others without approval, based on China’s Criminal Procedure Law. Passports and identification cards must be handed to police but the process shouldn’t exceed six months, according to the law.