At least three people have died and thousands have been relocated as a weakened Typhoon Haiyan brought gales and torrential rain to southern China's Hainan province and Vietnam.

The typhoon, which weakened into a tropical storm after killing thousands in the Philippines over the weekend, affected about 480,000 people in the southern island province of Hainan.

Three people died and 39,000 were relocated as the tropical storm destroyed dozens of homes and damaged hundreds more across Hainan, the provincial Civil Affairs Bureau reported on Monday.

Seven crew from a cargo vessel were missing off Hainan, which is close to Vietnam, the official Xinhua news agency reported.

The storm also affected the nearby southern Chinese provinces of Guangxi and Guangdong, the agency said.

It hit land in Guangxi's Ningming County on Monday morning with winds of about 120 kilometres per hour, bringing up to 291 millimetres of rain in 24 hours to the Beihai, Fangcheng and Shangsi areas.

The storm had made landfall in Vietnam's Quang Ninh province, about 160 kilometres north of Hanoi, at 5am (0900 AEDT) on Monday, with winds estimated at 118-133km/h, the National Centre for Hydro-Meteorological Forecasting said.

Heavy rains and floods hit the northeast and centre of the country, the National Committee for Floods Prevention and Control said. Some locations recorded rainfall of up to 271mm in the previous 24 hours.

There were no direct casualties in Vietnam, but 10 people died and 67 were injured in preparations, many from falls as they tried to secure their roofs from the coming storm, the National Committee for Floods Prevention and Control said.

Boat trips were suspended in popular tourist destination of Ha Long Bay, but were expected to resume on Tuesday, said Doan Manh Linh, a provincial tourism official.

It is high season for the bay, with about 2000 foreign tourists visiting daily.

The storm hit further north than expected, and northern provinces did not have much time to prepare, said Francis Markus, communications director for the Red Cross in East Asia.

"Thankfully the storm hasn't proved as serious as we were fearing, but there still could be serious flooding and landslides," he added.

On Saturday, authorities relocated about 500,000 people from central provinces ahead of the storm, according to local media.

Schools were closed and fishing boats off the coast of central and southern provinces were told to return to shore.