The Hong Kong Observatory issued the Standby Signal No 1 at 2:20 am on Saturday, after Tropical Cyclone Wipha moved to within 800 kilometres of Hong Kong a short while earlier.

It said it will consider issuing the Strong Wind Signal No 3 during the daytime on Saturday, with Wipha set to strengthen in intensity gradually.

"Wipha will be rather close to the vicinity of the Pearl River Estuary on Sunday and expected to skirt around 50 kilometres from Hong Kong," the Observatory said.

The weather watchdog said the weather will remain hot on Saturday, with strong winds to hit later in the day.

It also urged the public to stay away from the shoreline, as thunderstorms and heavy rain will pour over the SAR on Sunday.

The observatory will also consider issuing higher typhoon signals if needed.

Former HKO assistant director Leung Wing-mo, meanwhile, has warned of the "significant threat" posed by Wipha to Hong Kong.

The meteorologist cited data from weather prediction models, saying the storm could directly hit the SAR.

"It avoided the land mass of Luzon. In that way, it will preserve its intensity as a severe tropical storm, and then it will start to intensify as soon as it gets into the South China Sea," he said.

"By the time it comes closest to Hong Kong, it is already a full-blown typhoon, of typhoon intensity up to a maximum of 140 kilometres per hour. Judging from every aspect of this tropical cyclone, it's going to be a significant threat to Hong Kong."