
With wind speeds of up to 88 kilometres an hour, the storm was forecast to hit Quang Ninh province, 150 kilometres north-east of Hanoi, by 6 pm (1100 GMT) Thursday.
"All boats are not allowed to leave the shore, and the anti-storm and rescue forces must be standing by to ensure the safety of local people, tourists and properties," said Tran Dinh Hoa, head of the province's flood and storm department.
By 1 pm, the storm was 80 kilometres south-east of the province and was moving northward at 15 to 20 kilometres an hour, according to the National Weather Forecast Centre.
"We have warned all the tourist companies in the city about the storm and asked them to take all the tourist boats ashore," said Tran Van Hong, deputy director of Quang Ninh's Tourism Department.
Halong Bay is one of Vietnam's biggest tourist attractions, attracting more than 1 million foreign tourists each year to see towering rock formations rising from the sea and 1,500 small islands.
Touring by boat, often sleeping aboard overnight, is one of the most popular ways to see Halong Bay.
Southern China looked poised to bear the brunt of the storm, but Vietnamese officials said it was necessary to be prepared.
"We must all be aware of any possible happenings, especially landslides and flash floods, although this is not a very strong storm," Hoa said.
On Monday, flash floods caused by heavy rain killed three people and left one missing in Quang Ninh province.
Toraji is the first storm to hit Vietnam this typhoon season. More than 600 people were killed last year in Vietnam by storms and floods.
Deutsche Presse-Agentur