Thai government buildings flew flags at half mast on Friday to mourn the death of at least 38 people, including 22 children, after an ex-policeman burst into a daycare centre in a knife and gun rampage that left the nation shocked and seeking answers.

King Maha Vajiralongkorn and Prime Minister Prayut Chan-o-cha will be travelling to the province on Friday to visit the survivors, a government spokesman said.

Most of the children who died at the daycare centre in Uthai Sawan, a town 500km north-east of Bangkok, on Thursday were stabbed to death, police said, marking one of the worst child death tolls in a massacre by a single killer in recent history.

Police identified the attacker as a former member of the force who was discharged over drug allegations and who was facing trial on a drugs charge.

After the attack, he went home and shot dead his wife and child before turning his weapon on himself.

The age range of children at the daycare centre ranged from two to five years, a local official said.

“It’s a scene that nobody wants to see. From the first step when I went in, it felt harrowing,” Mr Piyalak Kingkaew, an emergency worker heading the first responder team, told Reuters.  “We’ve been through it before, but this incident is most harrowing because they are little kids.”

The former policeman had been in court earlier in the day and had then gone to the daycare centre to collect his child, police spokesperson Paisal Luesomboon told broadcaster ThaiPBS.

When he did not find his child there, he began the killing spree, Mr Paisal said.

“He started shooting, slashing, killing children,” Mr Paisal said.

Late on Thursday, pink and white coffins adorned with gold and bearing the bodies of children were loaded onto a truck and driven away in the darkness.

Thailand’s deputy prime minister Anutin Charnvirakul clasped his hands together and bowed his head as the truck left, followed by ambulances carrying the bodies of further victims.

“All Thai people, and all people around the world who know about this… will feel so depressed and saddened,” Mr Anutin said.

Meanwhile, a Reuters photographer saw the body of the shooter, Panya Kamrab, being moved in a bodybag from a van to a police station in the province.

“I don’t know (why he did this), but he was under a lot of pressure,” Panya’s mother told Nation TV, citing debt the former policeman had clocked up and his drug taking.

Photographs taken at the daycare centre by the rescue team and shared with Reuters showed the tiny bodies of those killed laid out on blankets. Abandoned juice boxes were scattered across the floor.

The body of one boy dressed in a Manchester United Shirt was seen on a Winnie the Pooh bed cover in a room with walls decorated with cartoon animals.

“He (the shooter) was heading towards me and I begged him for mercy, I didn’t know what to do,” one distraught woman told ThaiPBS, fighting back tears.

“He didn’t say anything, he shot at the door while the kids were sleeping,” another woman said, becoming distraught.

About 30 children were at the facility – a pink, one-storey building surrounded by a lawn and small palm trees – when the attacker arrived.

That was fewer than usual, as heavy rain had kept many people away, said district official Jidapa Boonsom.