The Observatory issued the Standby Signal Number 1 early on Friday, warning that the signal will remain in force until at least midday as Severe Tropical Storm Trami moves across the central and northern parts of the South China Sea.

It said Trami is forecast to stay more than about 600 kilometres from Hong Kong this morning, and its strong winds have not yet had an effect on the vicinity of the Pearl River Estuary.

The Observatory warned that the combined effect of Trami and the northeast monsoon would bring occasionally strong winds offshore and on high ground.

"However, as the prevailing winds over Hong Kong will mainly be northerlies, winds generally over Hong Kong will not strengthen significantly this morning," it said in a statement, noting that Hong Kong would be sheltered from much of Trami.

"The need to issue Strong Wind Signal No. 3 thereafter will depend on the distance between Trami and Hong Kong and the change in local wind strength," it said.

The Observatory said Trami is expected to move gradually towards Hainan Island, and predicted the local winds would weaken later on Sunday.

It said it would closely monitor Trami and assess the need to keep the signal in effect.

The Observatory warned people living in low-lying areas or places exposed to the sind should take precautions.

It advised the public not to engage in water sports and fishing vessels in the open sea should seek shelter.