The accident took place between the Paratuwa and Kapuduwa interchanges, the police spokesman said.
According to SSP Nihal Thalduwa, the bowser truck en route to Mattala from Kottawa had collided with a lorry carelessly parked on the expressway.
A 72-year-old who was travelling in the truck had died on the spot.
Meanwhile, the 61-year-old driver of the bowser truck died on admission to the Matara Hospital. He was identified as a resident of Gonawala area.
The truck driver’s assistant has sustained critical injuries and is currently under medical care at the Matara Hospital. – ada derana