According to the police the passengers of the van were returning home after attending a funeral when the accident took place.
The accident took place along the Kalutara – Horana road and the victims were residents of Ingiriya.
Among those killed were two children aged 11 and 6, the police said.
The two children and two women were burned to death.
The seven others, including three children aged 10, 1 and 7 a woman and three men, have been admitted to the Kalutara, Nagoda hospital for treatment.