Teachers in the nursery had put the children down for their nap by the time Panya arrived at around 12.30pm.
He attacked people in the courtyard, shooting some, slashing others with a long blade that farmers use for hacking crops.
Several people were killed there.
“Everything happened so quickly and there was blood everywhere,” said office worker Kittisak Polprakap, 29.
“I saw the wounded and dead sitting together at a table as if nothing had happened.”
People ran. Two female employees, Jidapha Boonsom, 48, and Saowaluk Keeta, 25, dashed into an office looking out onto the nursery.
Some staff called the police but were told they were busy elsewhere.
Panya shot twice at the nursery door and kicked it open, a witness told media. For about 20 minutes he went from room to room, shooting teachers and slashing the children with his machete.
Some teachers fled over a wall but not Supaporn Pramongmook, 26, who was eight months pregnant.
Another teacher, Maliwan Lasopha, tried to plead with Panya. They had played together as children.
He killed them both.