Hong Kong’s weather forecaster will issue the No 1 typhoon warning signal at 12.20pm on Friday as a low pressure over the northeastern part of the South China Sea intensifies into a tropical depression.

The Hong Kong Observatory said the tropical depression was expected to enter within 800km of the city, adding that the signal would remain in effect throughout the day.

“It will be slow-moving and maintain a distance of more than 400km from Hong Kong for the rest of the day,” it said.

According to the forecaster, the circulation of the tropical depression will be relatively small and is likely to linger over the northeastern part of the South China Sea during the weekend, before turning northwards in the general direction of the vicinity of the Taiwan Strait to the coast of eastern Guangdong.

It urged the public to avoid water sports and stay away from the shoreline over the weekend in the wake of swells.