HONG KONG — On many mornings throughout the pro-democracy protests that have convulsed Hong Kong, white Toyota Coaster vans with special black license plates have set out from city government buildings here to a tropical resort across the border in mainland China.

The drawn curtains of the speeding vans obscure Hong Kong officials, headed for the luxurious Bauhinia Villa in Shenzhen, where throngs of Communist Party officials from Beijing wait to plan details of the Hong Kong authorities’ handling of the demonstrations that have occupied major streets for nearly three weeks.