Hong Kong is on the brink of a record number of storm warning signals with the Observatory set to issue the 12th Standby Signal No. 1 of the year on Friday evening.

It is issuing the No. 1 signal at 7.40pm as Severe Tropical Storm Matmo comes within 800 kilometres of Hong Kong.

That 12th T1 tropical cyclone warning signal makes it the most since records began.

Previously, the highest number of T1 issued in a year was 11 in 1974.

At 4pm on Friday, Matmo was estimated to be about 280 kilometres north of Manila and moving into the central and northern South China Sea at about 25 kilometres per hour.

According to the current forecast, the storm will gradually move towards Hainan and intensify over the weekend.

The Observatory says it will assess the need for a higher warning signal on Saturday during the day, depending on Matmo's distance from Hong Kong, its intensity, and changes in local wind conditions.

Locally, the weather will become unsettled from late Saturday to Sunday, with windy conditions and occasional squally showers.

Seas will also be rough with swells.

The Observatory has also warned that more typhoons could occur later this year and urged the public to stay alert during the autumn.