A spokesman for a regional public affairs office said 26 deaths have been confirmed so far: 23 children, two teachers and a police officer.
According to Thai media reports, the attacker also used knives in the attack and then fled the building.
The photographs showed at least two bodies on the floor of the center covered in white sheets.
Several media outlets identified the assailant as a former police lieutenant colonel in the region, but there was no immediate official confirmation.
The Daily News newspaper reported that after fleeing the scene of the attack, the assailant returned home and committed suicide along with his wife and son.