Prime Minister Srettha Thavisin on Saturday called on authorities to speed up their investigation into the blaze at Win Process' hazardous waste storage plant in Rayong's Ban Khai district.
While inspecting the site, Mr Srettha demanded to know how long it will take to determine the cause. He was told that police could not enter the site to investigate until it was deemed safe to do so.
Mr Srettha was also informed that while the blaze was under control, there was a risk of it flaring up.
The fire broke out on Monday at the facility, affecting 100 villagers. Officials did not rule out arson as the cause of the blaze, noting the plant's electricity supply had long been disconnected.
A second blaze broke out on Wednesday night, with the authorities detecting high levels of dangerous chemicals in the air over the surrounding area.
There were about 10,00 tonnes of aluminium dross in the facility, Kanchalee Navickabhum, deputy director of the Pollution Control Department, said last week. The substance, when on fire, cannot be extinguished using water as it will cause a chemical reaction that will accelerate the blaze, he said.
A team of firefighters from the NPC company based in the Map Ta Phut Industrial Estate, which was sent to help extinguish the blaze, said the fire was under control and efforts were underway to ensure it would not flare up.
Mr Srettha has instructed the Department of Disaster Prevention and Mitigation to draw up a rehabilitation plan for the residents.
The Industrial Works Department and the Pollution Control Department were also ordered to monitor air quality and remove the waste.
Reports said the PM criticised the Industry Ministry for being slow to respond to the situation.