The blaze started around 12.30am in a five-storey house on Trung Kinh Street.
Three people are currently being treated at Giao Thong Van Tai Hospital. One, an elderly resident of the house, is in a serious condition. The other two are stable.
According to Cau Giay District police, the fire spread quickly and the whole property was engulfed in thick, black smoke.
Four people trapped in the building managed to escape by smashing windows and climbing to the ground floor.
Firefighters rushed to the scene but because of the location of the property, about 200m from Trung Kính Street, trucks were enable to get close and hoses had to be pulled into the alley to extinguish the blaze.
The house is about 100 sq.m, including the yard, and has 12 rooms for rent. The couple who own the building live in two rooms on the first floor.
It is understood there are seven members of that one family living there and 17 other people registered to rent rooms.
The identities and ages of the deceased have not yet been released.
The fire destroyed motorbikes, bicycles and electric bicycles stored on the ground floor. A steel frame and corrugated iron roof covering the yard collapsed.
By 4am, the fire was completely extinguished but Trung Kinh Street remained closed for several hours.
Lieutenant General Nguyen Van Long and Senior Lieutenant General Tran Quoc To, deputy ministers of public security, visited the scene.
Chairman of the Hanoi People's Committee, Tran Sy Thanh, said that units had been directed to investigate the cause of the fire, assess the damage and implement any necessary measures.
Viet Nam News
Asia News Network