"This heavy rain is the worst in Hanoi since 1984," said Duong Lien Chau, deputy director of the Central Hydro-Meteorological Forecast Center. "In some areas, this is the heaviest rainfall in more than 100 years."
With no typhoons in the region, the storm caught the capital by surprise. More than 500mm of rain fell in just three days.
"I did forecast the rain," said Chau, "but we did not expect it would be this heavy."
Most deaths were caused by drowning when the waters rose without warning. Streets quickly flooded, forcing people to navigate through water up to 1m high.
Several people, including children, died when they fell into open storm drains. There were reports that several people were electrocuted.
Hanoi is struggling to evacuate people still trapped in their homes. The city does not have an extensive rescue system, and many public vehicles have broken down.
With Hanoi's pumping system unable to cope with the heavy rainfall, the Army has been called in to help with rescue efforts. The city has just a single pumping station, which itself is partially under water. It will take another four to five days to pump out all the water - if the rain stops.
"We are trying our best to deal with the situation," Nguyen Thanh Giang, of the Hanoi People's Committee, told IRIN. "Thousands of people living near rivers are being evacuated to safety, as many river dykes in Hanoi are at serious risk of collapsing."
Giang said his office estimated the damage at US$180 million.
Enterprising farmers from outlying villages have brought small boats to Hanoi and are ferrying people through the city's flooded streets.
Trinh Thanh Thuy, a 30-year-old teacher, paid $1.20 for a boat to carry her motorbike 300m so she could continue her way to work.
"It is just like we are living in a flooded village," said Thuy. "Now I have a better understanding of how bad is it for people who get flooded in remote areas."
The worst is not over, according to authorities, with more rains predicted in the next few days. Although they expect them to be lighter, the ground is saturated and the city's many ponds and lakes are already overflowing their banks.
Food shortages are now predicted to hit Hanoi. The National Committee for Flood and Storm Control reports that 240,000 hectares of rice and vegetables have been damaged.
With several markets under water and transport paralysed, some food prices have more than tripled, according to residents. Shoppers reported being charged 10 times the normal rates.
Officials are also bracing for an outbreak of water-borne diseases as the waters recede. "There is a high risk of an epidemic as the city is flooded with polluted water," said Nguyen Huy Nga, director of the Preventive Medicine and Environment Department at Ministry of Health. "We are now watching for outbreaks of diarrhoea and dengue fever."