The Hong Kong Observatory is expected to issue the No 1 typhoon warning signal on Wednesday morning at the earliest and assess the need to raise the alert to a higher level the following day.

The forecaster said a broad area of low pressure over the central part of the South China Sea was consolidating at a distance of around 800km from the city and would gradually develop into a tropical depression on Tuesday afternoon or Wednesday morning.

“The Observatory will issue the No 1 standby signal on Wednesday morning at the earliest,” it said.

“The tropical cyclone is expected to move in the general direction of Hainan Island and the vicinity of the coast of western Guangdong in the middle and latter parts of this week.

“Depending on its distance from Hong Kong and its rate of development, the Observatory will assess the need of issuing a higher signal on Thursday.”