Four people were killed and three others injured when two containers of fireworks exploded at My Dinh Stadium before Hanoi's 1,000th birthday ceremony.
The incident happened at around 11:40 a.m. on Wednesday (October 6) during the capital's millennial celebrations from October 1 to 10.
Lieutenant General Nguyen Duc Nhanh, director of Hanoi Police Department, told Vietnam News Agency on the same day that the fire was caused by "mistakes" made during transportation.
He said eight fire trucks were sent to the site to put out the fire while injured people were brought to a nearby hospital for emergency treatment.
A Tuoi Tre reporter arrived at the scene around 10 minutes after the accident to find all the makeshift tents in My Dinh Stadium had burnt down and a nearby lawn on fire.
Thanh Minh, a bus driver leading a group of foreign tourists on a guided tour at the time, said he was standing some 200 meters the site when his bus's windows shattered. He suffered from minor burns on his back and hand, he told the paper.
The explosion sent metal debris flying and windows shattered at the Vietnam Sports Hospital and apartment blocks about 200 meters from the blast, AFP reported.
A woman who lives on the sixth floor of an apartment building in the area told the newswire that she was cooking when she heard "big explosions" and rushed to her balcony where she saw a plume of white smoke.
"The smoke was not like when someone burns something. Many people rushed down to the street to watch. The smoke came from the stadium area. There were about six or seven explosions," said the woman, who asked to remain anonymous.
Lt Gen Nhanh said the explosive was an "unfortunate accident but it would not affect the work of ensuring security during the Thang Long Hanoi's 1,000th birthday."
On late Wednesday, the spokesman for the Singapore Ministry of Foreign Affairs issued a statement in response to media queries over whether a Singaporean national was among the victims.
"An explosion occurred in the vicinity of the My Dinh Stadium in Hanoi. The Singapore Embassy in Hanoi is closely monitoring the situation and is in close contact with the local authorities," the statement said.
"Local authorities have informed the embassy that a Singaporean woman could be one of four fatalities. The embassy is working to verify this, and to ascertain if any other Singaporeans are affected," it added.
The containers in question are among three with fireworks inside due to be set off at My Dinh Stadium in a display on Sunday, the final day of the millennium celebrations. They were imported from Italy, the US and China by Hanoi International Manpower Supply and Trade Company Limited (INTERSERCO).
The fireworks display at My Dinh Stadium was designed to be the first in a series of 28 at various spots around the city. It was supposed to be the biggest-ever fireworks display in the country.
The ceremony will go ahead as planned on Sunday.