Firemen were today battling a blaze from a gas tank explosion that killed at least one person at a chemical plant in Thailand.

The blast ripped through the giant drum containing pyrolysis gasoline (pygas) at the petrochemical arm of public company Siam Cement Group (SCG) in Rayong at around 10:45 am local time.

Four injured staff were taken to hospital. One of them later died from his injuries.

The company said their staff along with state workers was investigating the cause of the explosion.

Dense black smoke from the flames filled the air, prompting the industrial estate to request reinforcement from nearby areas to contain the situation.

Residents at 2.20 PM reported hearing a loud explosion and observed chemicals spilling on the ground.

Employees and nearby residents were evacuated, and operations at the terminal were shut down.

The provincial public health office also has instructed all hospitals in the area to establish support centres for those affected by this incident.

Officials at the Industrial Estate Authority of Thailand declared a Level 2 Emergency Situation in the area.

An SCG spokesman said: 'In this incident, four individuals were injured and were promptly transported to the hospital under the care of medical professionals. 

'We later received a report of one employee succumbing to injuries. At present, the situation is still being controlled, and we are assessing the extent of damage. 

'An investigation into the cause of the incident is also underway.'

As of 3.30 PM, firefighters were working to control the fire within the area, but they had not yet been able to extinguish the flames.

Thai Prime Minister Srettha Thavisin announced the establishment of a war room to monitor the situation and ordered the Environmental Monitoring and Control Center to dispatch a truck to measure air quality.

Pyrolysis gasoline, also known as Pygas, is a byproduct obtained from the production of olefins. 

Rich in aromatic compounds, Pygas is prized for its high octane rating, making it a valuable component for boosting the octane level in gasoline production blends.