The police said a gas leak was believed to have caused the explosion at the Kalutara public burial grounds last evening.
The explosion took place when the body of a woman was about to be cremated.
According to the police the explosion took place when the body was placed and the gas was ignited.
The doors and roof of the building were damaged in the explosion.
Two people had also sustained minor injuries in the explosion and were admitted to hospital.
Measures were taken to transfer the body to another location to be cremated.
Further investigations are underway.