The observatory says it could issue the Standby Signal No 1 on Friday night as Tropical Cyclone Matmo is expected to come within 800 kilometres of Hong Kong.

"According to the present forecast, Matmo will move in the general direction of the vicinity of the coast of western Guangdong to the eastern part of Hainan Island over the weekend and intensify gradually," the weather forecaster said.

The observatory said it will assess the need for issuing a higher tropical cyclone warning signal during the day on Saturday.

Matmo is expected to become a severe typhoon and come within around 300 kilometres of Hong Kong over the weekend.