The Hong Kong Observatory has warned members of the public to take all necessary precautions, saying it will issue the No. 8 storm signal on Friday.

The strong wind signal No. 3 was issued at 3.40pm on Thursday as Super Typhoon Saola edges closer to the city.

At 3pm, the storm was estimated to be about 390 kilometres east-southeast of Hong Kong and is forecast to move west-northwest at about 10 kilometres per hour across the northeastern part of the South China Sea towards the coast of eastern Guangdong.

"According to the present forecast, Saola will be rather close to Hong Kong later tomorrow (September 1) and will pose a threat to Hong Kong. The Observatory will issue the Gale or Storm Signal No. 8 tomorrow," the forecaster said.

"Local weather is expected to deteriorate significantly, with heavy squally showers and violent winds, during the day tomorrow."

The government will hold a joint press conference at 4.30pm to brief the public on its storm-preparation work.