Eighteen of the deaths were in the capital Hanoi which has been lashed for days by the heaviest rainfall for 20 years, authorities said.
More rain was expected in Hanoi and several northern provinces Tuesday, but weather forecasters said it would be lighter than the downpours that soaked the capital over the weekend.
That would provide welcome relief to residents of Hanoi, where many streets were under three feet (a metre) of water and scores of businesses remained shuttered.
"I have been stuck in my house for the past three days," said Nguyen Manh Hung, a businessman who lives on a street in southern Hanoi where water reached his waist.
"It's unbelievable to see people navigating the street in boats and by horse-drawn carriages."
Vietnamese television quoted Hanoi Mayor Nguyen The Thao as saying it would take the city four or five days to pump excess water into the Red River - longer if heavy rains resume.
More than 20 inches (500mm) of rain have fallen on the city, the heaviest in more than two decades.
Authorities reported six deaths in the northern provinces of Vinh Phuc, Bac Giang and Thai Nguyen on Monday.
The central Nghe An province was worst-hit after 10 more bodies were recovered Monday, bringing the death toll there to 22, said provincial disaster official Nguyen Dinh Thuy.
Rains continued to fall in the province, preventing rescue workers from accessing affected areas, Thuy said.
"Water is everywhere. Many parts of the province are still isolated," said Thuy.
"We have to use motorboats to rush food aid to villagers, who have been in hunger for several days."
Floods have inundated more than 100,000 homes across northern and central Vietnam, the national committee for flood and storm control said on its Web site.
More than 590,000 acres (240,000 hectares) of rice and vegetables have been destroyed and about 100 miles (170km) of rural roads damaged, it said.
