Sanan had previously said the blast was believed to have been caused by a “technical error” during welding.
Police on Sunday said they were still investigating the cause, adding they believed the facility was not licensed to store fireworks.
Provincial commander Police Major General Chalermporn Khamkhiew said firecrackers had been delivered shortly before the explosion.
“We are investigating if those firecrackers were transported legally or illegally,” he said.
“As of now, we do not see any licence for possession of firecrackers or firecracker sales,” he said.
“We assume the factory has no licence.”
The blast detonated roughly 1,000kg of gunpowder, he said, leaving two holes roughly 2m deep and 6m wide.
“We have issued a summons to the owner of the factory with the charge of negligence, which caused the accident,” said Colonel Suthawet Thareethai, police chief in Muno district.
“We are waiting for him to come.”
Officials said a command centre had been established not far from the scene, and authorities had already received 365 complaints from those who had been injured or had their homes and property damaged.
Damage to government offices and private schools was also reported, they added.
“NOTHING LEFT”
Police said that of the 115 people injured in the blast, 106 had been discharged. The condition of those remaining in hospital was not known.
A fire sparked by the explosion was brought under control late on Saturday.
On Sunday, residents surveyed the wreckage where their homes once stood as officers and emergency crews sifted through the rubble.
“I have nothing left,” said Samsueya Chuenchompoo, whose house was destroyed.
“I don’t even have a roof over my head now. When there was a flood, I still could survive but now I really have nothing left.”
Another affected resident, Sudarat Nooliteh, said her home had disappeared.
“I have no place to sleep. I have no food. I have no money,” she said.
Southern military commander Lieutenant General Santi Sakhutanark said the army would “provide manpower and equipment” for the recovery and clean-up operation.
Explosions at workshops producing firecrackers and other pyrotechnics are not uncommon in Thailand.
Saturday’s deadly blast comes just five days after 11 people were reportedly injured when a fireworks factory exploded in the northern city of Chiang Mai.
The Southeast Asian kingdom also has a poor safety record in the construction sector and deadly accidents are common.
Last month two people were killed when a bridge under construction in Bangkok collapsed onto traffic.
