GUANGZHOU, China — Huobi, one of the world’s largest cryptocurrency exchanges, said it has ceased new account openings for mainland Chinese users after Beijing renewed a crackdown on virtual currencies.The People’s Bank of China declared all virtual currency-related activities illegal including trading on Friday. The Chinese central bank also took aim at overseas exchanges providing services to mainland China users.Huobi, one of these exchanges, said on Sunday that it would end account registrations for new mainland Chinese users. The company will also gradually retire existing accounts of mainland Chinese users by midnight on Dec. 31, 2021.cnbc.com