Hyderabad, Aug 24 (IANS): The death toll in the major fire that broke a day ago in the Hindustan Petroleum Corporation Ltd (HPCL) refinery in Andhra Pradesh's coastal city of Visakhapatnam rose to four, police said Saturday.

Five workers are still reported missing, officials said, adding that 39 people are under treatment in hospitals, many of them battling for life.

Personnel from the National Disaster Response Force (NDRF) joined the search operation at the mishap site, the diesel hydro sulphurisation expansion project.

According to officials, two people died on the spot, while two others succumbed at a hospital. Majority of the injured sustained serious burn injuries.

The fire broke out after a major blast in an under-construction cooling tower in the state-owned HPCL refinery Friday evening.

About a dozen fire engines controlled the fire, not allowing it to spread to other parts of the refinery.

With five workers still reported missing, authorities have opened a control room at the district collectorate. Relatives of the missing workers staged a protest Saturday at the main entrance of the refinery.

About 4,000 employees of the refinery were boycotting their duties Saturday to demand proper safety measures at the refinery.

Union Minister of State for Petroleum Pannabaka Lakshmi visited the refinery and spoke to the officials about the disaster.

The cause of the fire is still not known. Chief Minister N. Kiran Kumar Reddy has ordered a probe.