Police said they have arrested a man suspected of pushing a boy into the sea in To Kwa Wan last weekend.

The suspect, 23, was arrested on Tuesday.

Officers said the man and the boy, 9, do not know each other.

At a press briefing on Wednesday, chief inspector Cheung Lok-chuen said officers will continue their investigation by looking into the man's background and mental state, as well as a possible motive.

"The force would like to remind the public that assault occasioning actual bodily harm is a serious offence, with the highest penalty being three years imprisonment upon conviction," Cheung said.

"It is fortunate that the boy suffered relatively minor injuries. Otherwise, the suspect will face more serious charges and punishment."

Police said the boy and his mother were fishing at Hoi Sham Park on Saturday and was pushed into the sea when she was not looking. He managed to swim ashore on his own.

Officers called on possible witnesses to come forward and provide more information.