The observatory issued the standby signal number 1 on Wednesday afternoon as Super Typhoon Saola moves closer to Hong Kong and enters within 800km of the territory.

The observatory also said the strong wind signal number 3 will be issued on Thursday.

It said according to the present forecast track, the storm will maintain a distance of more than 300km from Hong Kong on Wednesday evening and Thursday morning, and the standby signal will remain in force before noon on Thursday.

And as Saola edges closer to the coast of eastern Guangdong, winds will strengthen gradually and a higher signal will take effect.

"Under the influence of the northeast monsoon, there is still uncertainty in the track and intensity of Saola. It may make landfall over Guangdong or move westwards across the coastal waters of Guangdong," the observatory said.

Saola was centred off southern Taiwan on Wednesday afternoon and it's forecast to move west-northwest across the northeastern part of the South China Sea.