WARNNING: Contains graphic content.

At least 38 people are dead, including as many as 23 children, after a cold-blooded killer broke into a pre-school in Thailand and butchered the kids as they slept.

Reportedly, just a single child at the centre survived the attack.

Former police officer Panya Khamrap, 34, was armed with a shotgun, a pistol and a meat cleaver when he burst into the nursery 480km north east of Bangkok and shot dead adults including an eight-months pregnant woman.

He then broke into a locked room and stabbed the sleeping children to death. Some were as young as 2 years old.

According to reports, Khamrap – who had been sacked from the police over drug allegations and was due in court on the morning of the attack – arrived at the nursery and became agitated after realising his child was not there.

The shooter fled in a white Toyota pick-up truck, attacking others as he left, before reportedly killing his wife and child at their home, which he set on fire. Another three adults were found dead inside the home.

Media reports suggest the gunman then shot and killed himself.

Panya Khamrap - The suspected gunman that open fired at the preschool in Thailand. Photo / Nong Bua Lamphu Provincial Public Relations Office.

In total, 38 people have been killed, including the shooter. Twenty-four bodies, including 19 boys, three girls and two adults, were found at the daycare centre. It is the deadliest mass killing in Thailand's history.

At least 12 other people were injured.

Local reports suggested that Khamrap was fired from the police for failing a drugs test and that he faced court before the attack.

Police spokesman Paisan Luesomboon told broadcaster ThaiPBS that Khamrap went to the childcare centre to find his child, who was not there.

"He was already stressed and when he couldn't find his child he was more stressed and started shooting," Paisan said.

Khamrap was last seen driving a white-four door Toyota pick-up truck with Bangkok registration plates, before he was found dead.

'Thought it was fireworks'

A teacher at the daycare who survived the attack said Khamrap pointed the gun at her head, but she was able to climb over a wall to escape.

"I knew it was a gun because I heard multiple gunshots, and then I saw him put in the bullets and point the gun at me.

"I called the teacher, and the teacher was hugging the child. He kicked the mirror and I climbed the walls and asked for help.

"He was inside the child centre for a long time. He used a knife and cut all the kids' heads. He was carrying a small gun.

Coffins are seen outside a preschool. Photo / Getty

"I didn't know he was going to kill the kids. I thought he was gonna come out but he stayed inside a long time. He used a knife and stabbed all the kids.

"He also stabbed a pregnant teacher. Only few months til she gives birth. He stabbed my staff. That's all I know."

"The shooter came in around lunch time and shot four or five officials at the childcare centre first," local official Jidapa Boonsom told Reuters.

"At first people thought it was fireworks," she said.

Thai Prime Minister Prayuth Chan-ocha described the shooting as "a shocking event".

Shooter's drug issues

Khamrap was sacked from the police in January this year after being caught with pills containing meth and caffeine, reports said.

He had previously been warned for drug use.

He had served as a police officer for 10 years.

Colleagues claimed he had mood swings and was not popular at work.

Khamrap was said to have pulled a pistol on a bank manager who found him asleep, parked outside his bank when he was supposed to be guarding it, The Nation Thailand reported.

He was also said to have argued with his wife after he supposedly had an affair, and was reported to have argued with a neighbour after having raucous house parties.

Worst killing in Thai history.

Mass murders in Thailand are extremely rare.

The last time so many people were killed in a single incident was in 2021 when a soldier killed 21 people and injured dozens more in Nakhon Ratchasima.

In the past year, there have been at least two other cases of shooting murders by serving soldiers, according to the Bangkok Post.

Distraught family members of the victims. Photo / Twitter.

And in 2020, in one of the kingdom's deadliest incidents in recent years, a soldier gunned down 29 people in a 17-hour rampage and wounded scores more before he was shot dead by commandos.

That mass shooting was linked to a debt dispute between gunman Sergeant-Major Jakrapanth Thomma and a senior officer, and the military top brass were at pains to portray the killer as a rogue soldier.

Location map. Photo / AP