The observatory issued the Standby Signal No 1 at 10.20pm on Saturday, warning that a tropical depression was approaching the territory.

"The tropical depression is expected to move in the general direction of the vicinity of Hainan Island. Under the combined effect of the tropical depression and the ridge of high pressure over southeastern China, local winds will strengthen on Sunday," it said.

Forecasters said the No 1 signal would remain in force until at least 9am on Sunday.

"Depending on its [the storm's] distance from Hong Kong and the change in local winds, the observatory will assess the need to issue the Strong Wind Signal No 3 between 9am and noon on Sunday," they added.

The observatory said showers would increase gradually on Sunday, and there would still be some heavy showers around on Monday and Tuesday.