Pol Captain Somboon Phattarawongwiset, deputy inspector of Sai Yok Police Station, said the fire started at 11 minutes after midnight.
Some 20 fire engines took about five hours to control the blaze. They managed to control the fire at 5am on Saturday.
Workers had to rush to move planks that had not yet caught fire out of the mill’s compound. The blaze spread through piles of sawdust and processed wood quickly.
The sawmill is owned by Kesinee Mongkoltip, 49.
Somboon said forensic evidence officers have yet to establish the cause of the fire.