The city of Sanya on Hainan Island, renowned for its seafront resorts and sandy beaches, closed tourist attractions, shuttered businesses and suspended public transport on Sunday as it braced for an intensifying Typhoon Kajiki.

The tropical cyclone was about 200 kilometres southeast of Sanya at 9 am, packing maximum sustained wind of 38 metres a second near its centre, the National Meteorological Center said.

Kajiki is likely to strengthen as it moves northwest at approximately 20 kilometres an hour, with a peak wind speed as fast as 48 metres per second, the state weather forecaster said.

The storm could make landfall along the southern coast of Hainan from Sunday afternoon to evening, or skirt the southern coastline before heading towards Vietnam in the west.

The centre forecast heavy rainfall and strong winds in Hainan and nearby Guangdong province, as well as Guangxi, with areas in Hainan set to receive as much as 400 millimetres of precipitation.

Sanya issued a red typhoon alert on Sunday morning, the highest alert in the nation's colour-coded warning system.

All classes and construction are suspended, and shopping centres, restaurants and supermarkets are closed from Sunday.

Vessels have been ordered to cease operating in Sanya's waters. (Reuters)