Officials in Hanoi suspended a bus company's operations after one of its vehicles flew into a gorge during an unapproved trip through Vietnam’s northern highlands on Monday night.
At least a dozen were reported dead, as of press time.
Nguyen Hoang Linh, deputy director of the Hanoi Transportation Department, said they have revoked the Sao Viet Company's transportation license and suspended its operations in and around the capitol, Tuoi Tre newspaper reported.
Khuat Viet Hung, vice chairman of the National Committee for Traffic Safety, told news website Dan Tri that the bus was licensed to travel between My Dinh Bus Station in Hanoi and Lao Cai--the capitol city of the namesake province.
“The vehicle was not allowed to continue on to Sapa,” he said.
The bus tried to avoid a car traveling in the opposite direction and plunged down a 200 meter gorge on its way back from Sapa, a popular tourist destination 38 kilometers from Lao Cai.
Two pregnant women were among the dead.
Sao Viet's director, Do Van Bang, admitted the trip had been illegal but said: “The bus went to Sa Pa due to passenger demand.”
Bang said his company’s business license allowed him to conduct tourism services.
Investigators said the bus was also overloaded, carrying 53 people including two drivers and a driver's assistant. It was designed to accommodate a maximum of 47 people.
A recording device on the bus was switched off one hour before the accident happened at around 7:30 p.m., Dan Tri quoted investigators as saying.
Prime Minister Nguyen Tan Dung sent his condolences to the victims and their families on Tuesday, while praising the swift action of the rescue workers.
Transport Minister Dinh La Thang and Deputy Health Minister Nguyen Thanh Long accompanied a team of rescue workers and doctors to the site in the early hours of Tuesday morning.
The team counted 41 injured, including the driver who suffered multiple injuries.
Doctors in Hanoi have already operated on five of the nine most serious cases.
One woman suffered multiple injuries including fractures to her pelvis, thighs, spinal cord and skull.
Another young man was led away from the crash site with a length of wood protruding from his head. The stick had allegedly punctured his eye and entered his brain.
The victims were rushed to Lao Cai hospitals but Thanh ordered all severe cases to be forwarded to Hanoi.
Thang instructed the police to check if the driver was under the influence of alcohol.
Forces are also working to identify the victims.
Bang said the passengers were office workers and students -- most are from Hanoi; a few are from Ho Chi Minh City.
He said the two deceased pregnant women were likely Hanoians.
The traffic safety committee has already paid the bereaved families VND5 million (US$236) and the injured VND2 million ($94) each.
The number of travelers surged during this year's Independence Day (September 2) holiday, which fell close to the weekend.
Like other transport companies, Sao Viet hired extra vehicles, including the unlucky bus, which left Hanoi on Saturday evening and safely traveled some 350 kilometers to Lao Cai before tragedy struck.
Official figures show that during the first three days of the national holiday, 123 traffic accidents occurred across the country, leaving 66 people and injuring 70 others.
Road accidents are not new to Vietnam, especially on overnight buses.
Narrow highways, poorly maintained vehicles and a general disregard for road safety and traffic rules are often the cause of most fatalities.
Last year, Vietnam logged 29,385 traffic accidents that claimed 9,369 lives and left about 29,500 others injured. In 2012, traffic accidents killed 9,424 people nationwide.