Tropical Storm Haiyan, which killed thousands as a typhoon in the Philippines, has made landfall in north Vietnam, near the border with China.
It still carried gusts of up to 157km/h (98 mph) as it arrived close to the Ha Long Bay tourist destination.
Nearly 900,000 people have been evacuated from regions at risk. Reports say at least 13 people have been killed and 81 injured.
China issued a typhoon alert for Hainan island and other southern provinces.
Chinese rescuers found two bodies off Hainan on Monday, the state-run Xinhua agency reported. They are believed to be sailors from a cargo vessel missing in the South China Sea since Sunday.
Another five crew members are still unaccounted for.
Vietnamese state media said that although at least 13 people had died, the fatalities appeared to have taken place during preparations for the storm, before it made landfall.
One of those killed was a journalist who died in an accident on her way to cover the storm, reports said.
The typhoon has decreased markedly in strength from the Category Five storm that swept through the Philippines in a day, causing mass destruction.
It is now classified as a severe tropical storm.
By 21:00 GMT on Monday, as it heads into China, it will have become a tropical depression.
Rainfall will be the main hazard. A 48-hour accumulation of 100mm to 200mm is expected, with up to 400mm over high ground.
Widespread flooding is a possibility, including in Vietnam's capital, Hanoi.
Oxfam's Vietnam director, Andy Baker, told the BBC: "We've had fairly intense rain across much of northern Vietnam, including here in Hanoi where I'm based, and there are concerns about flooding... there's been something of a storm surge of perhaps 3-4m (13ft) higher than usual."
International Federation of Red Cross representative Francis Markus, who is in Hanoi, told the BBC: "We need to be thankful that this storm system has weakened as it's hit Vietnam.
"But at the same time we also can't be complacent because having travelled over such a wide expanse of sea, it's picked up a huge amount of moisture and so we can expect very heavy rainfall with potential flooding and landslides and other dangers."
A resident of Hanoi, Nguyen Thi Uyen, told AFP he had dashed to the supermarket to stock up.
"There was not much left on the shelves... people are worried, buying food to last them for a few days."
There are reports of rising prices in the capital.
Haiyan earlier swept over Vietnam's Con Co island, 30km (18 miles) off the coast of central Quang Tri province.
"All 250 people on the island, including residents and soldiers, were evacuated to underground shelters where there is enough food for several days," the Tuoi Tre newspaper said.
Boats have been ordered back to port along many coastal regions. Several hundred domestic and international flights have been cancelled. Schools have been closed for Monday in many parts of the north.
The authorities have moved 883,000 people in 11 central provinces to safe zones, according to Reuters.
Some people have complained that the warnings have come too late.
In China, Xinhua reported that the National Meteorological Center had issued a red typhoon warning - the highest alert in its four-colour typhoon warning system.
More than 13,000 people were evacuated from the major tourist resort of Sanya on Hainan.
More than 200 flights at Hainan's airports have been cancelled or delayed.
The typhoon passed by the south-western tip of Hainan as it headed for landfall on the Vietnam coast close to the China border, the Hong Kong Observatory's typhoon tracker showed.
Xinhua also said that eight people had died after being swept out to sea in northern Taiwan by waves attributed to Haiyan.
The typhoon killed up to 10,000 people in one area of the Philippines alone, with rescuers as yet unable to reach many other cut-off regions.
It brought sustained winds of 235km/h (147mph), with gusts of 275 km/h (170 mph), with waves as high as 15m (45ft), bringing up to 400mm (15.75 inches) of rain in places.
Reproduced under licence from BBC News © 2013 BBC