HONG KONG—The chairman of Macau’s largest junket operator was questioned by police in the gambling hub after authorities in mainland China issued a warrant for his arrest, the Macau government said on Saturday.

Alvin Chau, the chairman of Suncity Group Holdings Ltd. , was being held for questioning by police in Macau on Saturday after authorities in the eastern Chinese city of Wenzhou issued an arrest warrant alleging that he ran an illegal cross-border gambling syndicate, according to a statement issued by the Macau government.