According to a report from Hanoi Police Department, the fire broke out at about 7.45 am at a three-storey house on Thanh Cong Street.
"The fire started from the first floor and quickly spread to other floors," the police said. "Some neighbours tried to put out the fire but it just spread so fast. They called the fire police who came and controlled the fire at 8.15 am."
Police then found four bodies inside the house. They were identified as Nguyen Thi Xuyen, 67, and her three grandsons aged 10, 8 and 4.
Initial investigations showed that the fire broke out from a motorbike on the first floor.
On May 12, another fire occurred at a bar in the northern city of Haiphong, killing three staff members.
The authorities are investigating the causes of the fire.
