The Observatory said on Friday it will consider issuing the Standby Signal No. 1 as soon as tonight as a tropical cyclone is expected to develop and be within 800 kilometres away from Hong Kong.

"The area of low pressure near Luzon is currently about 800 kilometres away from Hong Kong. It is expected to develop into a tropical cyclone tonight [Friday] to tomorrow [Saturday] morning," it said.

According to the present forecast, the weather forecaster said, the tropical cyclone will intensify progressively and move towards the coast of Guangdong in the next couple of days, but there are uncertainties in its intensity and speed of movement.

"Depending on the intensity of the tropical cyclone, the distance of its strong winds from the territory and the changes in local winds, the Observatory will assess the need [to issue] higher tropical cyclone warning signals on Sunday," it said.

The Observatory said the weather will be extremely hot during the day, with temperatures reaching about 35 degrees Celsius in urban areas and a couple of degrees higher in the New Territories.