The observatory issued the Standby Signal No. 1 at 9.20pm on Wednesday as a tropical cyclone edges closer to Hong Kong.

The forecaster said the storm is expected to intensify gradually while moving across the northeastern part of the South China Sea over the next few days.

It is heading in the general direction of eastern Guangdong.

"Under the influence of the northeast monsoon, the tropical cyclone will then turn westwards, edging closer to the vicinity of the Pearl River Estuary," the weatherman said.

"However, there are uncertainties in its landfall position and intensity. As its circulation is relatively small, the tropical cyclone will only bring significant impact to local weather when it gets relatively close to Hong Kong."

The observatory said it will assess the need for higher tropical cyclone warning signals on Thursday and Friday, depending on the storm's intensity, the distance of its strong winds from Hong Kong and changes in local wind conditions.