The fire was reported at around 2.06 am on September 16 at a house in an alley off Van Cao Street in Tay Ho Ward.
Hanoi police dispatched five fire engines and nearly 40 firefighters and rescuers to the scene.
The four-storey house has a floor area of about 60 square metres on each level. Four people had escaped by the time emergency crews arrived, while others remained trapped inside, police said.
The blaze was largely brought under control by around 2:30 a.m., preventing it from spreading to neighbouring properties, and was fully extinguished at 2.45 am.
During a search of the house, firefighters found five people dead. Their bodies were handed over to medical personnel.
Hanoi People's Committee Chairman Vu Dai Thang arrived at the scene early on Wednesday and ordered relevant agencies to assist the victims' families and deal with the aftermath.
Authorities are investigating the cause of the fire.