Rescue workers transport a victim to hospital in Hanoi on Wednesday. AFP

Dozens of people died in a fire at an apartment block in Vietnam's capital Hanoi, state media said Wednesday, with witnesses reporting screams from inside and a small boy thrown from the building.

The fire started just before midnight on Tuesday (1700 GMT) in the parking floor of the 10-storey building, an area packed with motorbikes, witnesses said.

Authorities rescued about 70 people and rushed 54 to hospital, including "dozens of dead", the official Vietnam News Agency said.

At least three children were among the dead, Viettimes, an online state newspaper, reported.

"I heard a lot of shouts for help. We could not help them much," said Hoa, a woman who lives near the block and gave only one name.

"The apartment is so closed with no escape route, impossible for the victims to get out," she told AFP at the site.

Smoke rises from a building in Hanoi, Vietnam, on Wednesday. AP

Photos by AFP photographers on the scene overnight showed flames and smoke billowing from barred balconies.

The blaze was out by Wednesday morning, as rescuers still struggled to access the building, which is down a narrow alley in a residential area of southwest Hanoi.

The building's small balconies were surrounded by iron bars, with the apartment block having only a single exit -- and no emergency ladder on the outside.

Around 150 people lived in the complex, authorities said.

Another witness, Huong, said a small boy was thrown from a high floor to help him escape the flames.

Rescue workers transport a victim to hospital following a major fire in Hanoi on Wednesday. AFP

"I was about to sleep when I smelled something. I went outside and saw the fire," she said.

"The smoke was everywhere. There was a little boy thrown from a high floor, I don't know whether he survived or not although people used a mattress to catch him," she said.

The deputy prime minister, Tran Luu Quang, visited the scene Wednesday morning, state media said.

Vietnam has experienced several deadly fires in recent years, frequently at entertainment venues.

A year ago, a blaze in a three-storey karaoke bar in commercial hub Ho Chi Minh City killed 32 people.

This handout photo shows rescue workers carrying victims following a major fire at an apartment block in Hanoi. AFP

At least 17 people were injured in that fire, with the owner arrested on charges related to breaching fire prevention regulations.

In the aftermath, the prime minister ordered an inspection of all high-risk venues.

Thirteen people died in 2018 after an apartment complex, also in Ho Chin Minh City, caught fire.

Another 13 died in 2016 in a karaoke venue in Hanoi following a fire.

Southeast Asia frequently sees deadly fires with accidental conflagrations common, a result of lax safety standards.