The Standby Signal No 1 will remain in effect on Wednesday night and Thursday morning unless tropical storm Wutip rapidly intensifies and strong winds become widespread across the region, the observatory said.

Acting senior scientific officer Shum Chi-tai said Wutip is located approximately 650 kilometres southwest of Hong Kong as of 5pm and forecast to move in the general direction of Hainan and intensify.

"According to the present forecast, although local winds will weaken slightly at first on Friday, they will become southerlies gradually afterwards and there will be occasional heavy squally showers," he said.

"Winds may be generally strong over the territory."

"Depending on Wutip’s intensity at that time, distance from Hong Kong and the change in local wind conditions, the observatory will assess the need to issue the Strong Wind Signal No 3 on Friday."