BEIJING (Reuters) - China's central government firmly supports the Hong Kong government in passing an extradition law allowing people to be sent to mainland China for trial, the foreign ministry reiterated on Wednesday.

Ministry spokesman Geng Shuang told a news briefing in Beijing that any actions that harm Hong Kong are opposed by mainstream Hong Kong public opinion. He also urged the United States to speak and act with caution regarding Hong Kong.

Tens of thousands of Hong Kong demonstrators surrounded the Chinese-ruled city's legislature, forcing it to postpone a second round of debate on the extradition bill.

(Reporting by Ben Blanchard; Writing by Michael Martina; Editing by Clarence Fernandez)