Yagi triggered floods and landslides on the main Philippine island of Luzon this week, leaving at least 13 dead, according to official figures.

The tropical storm intensified into a super typhoon as it tracked west across the South China Sea, China's Xinhua news agency said, packing winds of up to 209 kilometres (130 miles) per hour as it headed for Hainan.

"Hainan upgraded its emergency response to Yagi to the highest level at 11:30 am Thursday, according to the provincial disaster management authority," Xinhua said.

The typhoon is expected to make landfall on Friday afternoon in either Hainan or neighbouring Guangdong.

Work, school and local transport services were suspended from Thursday noon (0400 GMT) in Haikou, Hainan's capital.

Hong Kong's weather observatory issued the third-highest typhoon warning at 6:20 pm (1020 GMT), limiting public transport across the finance hub.

The finance hub's stock exchange halted after-hours trading citing the typhoon warning, while 38 flights were cancelled at Hong Kong's airport Thursday.

Classes at primary and secondary schoools will remain suspended on Friday, the Education Bureau said.

"Yagi will remain at super typhoon intensity and skirt around 300 kilometres (186 miles) to the southwest of Hong Kong tomorrow morning," the observatory said.

"Gale winds associated with Yagi are expected to affect the vicinity of the Pearl River Estuary tonight and tomorrow morning."

After southern China, Yagi will move towards Vietnam, on course to hit the northern and north-central regions around the famed UNESCO heritage site Halong Bay.

Vietnamese authorities urged around 2,200 tourists on coastal islands to return to the mainland ahead of the storm's arrival.

They warned heavy rains may cause widespread flooding in mountainous and urban areas, including the capital Hanoi.

The country's meteorological agency issued a storm warning earlier on Thursday, and the government mobilised more than 2,700 military personnel for storm response.

Coastal provinces are planning a sailing ban on Friday, while Vietnam's mountainous provinces were ordered to prepare rescue vehicles.

burs-hol/dhw