HONG KONG - A Hong Kong police officers' union has urged police chiefs to better protect rank-and-file staff as the city braces for rolling protests in coming weeks over a controversial planned extradition treaty to mainland China.

In a letter to force management seen by Reuters, the Junior Police Officers' Association said it wanted guarantees that police chief Stephen Lo and his senior managers could ensure their "safety and mental health".

Three police officers were being treated in hospital on Monday for injuries sustained in skirmishes on Sunday.

Hong Kong has been rocked by large and sometimes violent street protests over the now-suspended extradition bill that would have allowed criminal suspects in Hong Kong to be sent to China to face trial in courts controlled by the Communist Party.

Critics of the bill say it threatens Hong Kong's rule of law and want it completely withdrawn and Lam to step down. -Reuters