Officials in Quang Ninh said Haiyan made landfall in the northern Vietnam province 2 hours earlier than predicted by the nation's weather service, Tuoi Tre newspaper reported.
The three missing people were part of a four-person crew on a cargo ship that sank during the storm off Cam Pha Monday, officials said. One person was rescued.
Haiyan, which left a trail of destruction and death in the Philippines before heading toward Vietnam, had sustained winds between 55 mph and 72 mph with gusts as high as 92 mph in Ha Long City and Co To Island.
The storm smashed 18 houses, ripped roofs off 525 houses, sank 16 ships, destroyed two antenna towers, ruined acres of crops and uprooted numerous trees, Tuoi Tre said.
The storm moved into China's southern Guang Xi province, where it is expected to weaken to a tropical depression.
Haiyan, known in the Philippines as Yolanda, showed no mercy to those in its path or its sphere of influence, extending to Taiwan and mainland China, while the victims and authorities in the Philippines faced the grim task of counting the dead -- feared to be in the thousands -- and assessing the huge damage in the storm's wake.
However, even prior to the arrival of the juggernaut and forecasts that it was weakening, at least six people were reported to have died after falling from trees or rooftops as they worked to secure their homes, the Vietnam News Agency reported.
Authorities in Vietnam evacuated hundreds of thousands of people in the path of the storm. Schools in Hanoi were closed Monday. In the port city of Haiphong, more than 2,000 vessels had been called ashore.
At least eight people were killed during the weekend in northeastern Taiwan after being swept into the sea by waves, some as tall as 26 feet stirred up by Haiyan, China's Xinhua news agency reported. Eight others, who were rescued, suffered injuries.
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