Typhoon Chanchu, the strongest typhoon on record to enter the South China Sea in May and packing heavy rain and winds up to 170 kph (106 mph), made landfall between the cities of Shantou and Xiamen and was heading northeast, the Hong Kong Observatory said.

China's coastal provinces of Guangdong and Fujian took the full brunt of the storm.

"Two children died when the houses they lived in collapsed and another two elderly people were injured," Xinhua said, quoting local government sources.

Almost all roads in Shantou were flooded and there had been several blackouts, Xinhua said.

Vietnam's National Search and Rescue Centre, in a bulletin carried by the Voice of Vietnam radio station, said 99 fishermen aboard 11 ships last made radio contact on Wednesday morning some 160 nautical miles (300 km) south of Hainan island, then in the storm's path.

Pham Quoc Te, a senior official at the centre, told Reuters the coast guard and navy were leading the rescue mission, and officials had contacted authorities in China and Hong Kong for help.

"Because the typhoon is still very strong at the moment, it will take time for rescue teams to locate and approach the missing ships," Te said.

Typhoons, drawing strength from warm water, roar into China from the South China Sea every year between May and September, losing power once they make landfall, unless they veer back to sea.

More than 630,000 people had been evacuated in the path of Chanchu, which killed at least 37 people when it swept through the Philippines at the weekend.

The eye of the storm crossed the Chinese coast halfway between Hong Kong and Taiwan, both often the victims of direct hits.

An ore-carrying Belgian ship with eight crew members was stranded offshore and a Chinese rescue vessel was expected to reach it on Thursday, state television said.

In Taiwan, rescuers winched to safety the crew of an oil tanker that had run aground off the coast of Kaoshiung after being hit by a large wave, television footage showed.

In the Philippines, Chanchu killed at least 37 people last weekend and "affected" about 53,300 people in wide areas of Luzon and the Visayas, the National Disaster Coordinating Council said.