Wipha was located around 280 kilometres (175 miles) southeast of Hong Kong as of midnight (1600 GMT), according to Hong Kong's weather observatory.

The observatory has hoisted the T8 warning signal, meaning that "winds with mean speeds of 63 kilometres per hour or more are expected".

The storm was expected to keep intensifying, moving across the northern part of the South China Sea and edging closer to the coast of China's Guangdong province.

"There will be frequent heavy squally showers and thunderstorms over the region. Seas will be high with swells," the observatory added.

China's Hainan and Guangdong provinces were also put on high alert, state news agency Xinhua reported Saturday.

More than 250 flights servicing Hong Kong had been cancelled as of late Saturday, according to the website of the city's international airport.

Hong Kong's Airport Authority asked travellers to prepare for "significant flight cancellations or delays" and said that no passenger flights are expected to depart the city before Sunday noon.

Authorities suspended Sunday's classes at all day schools and daycare centres.

Bus services are expected to be halted until midday Sunday.

Wipha brought heavy rains and flooding to the Philippines and two people have been reported missing, according to the country's National Disaster Risk Reduction and Management Council.