Commandos on Sunday killed a soldier after he carried out a shooting rampage in Korat that left at least 20 people dead, police said.

They said he had been killed at the Terminal 21 shopping mall in Nakhon Ratchasima where the gunman, who earlier took hostages, was holed up for 17 hours.

"He was shot dead thirty minutes ago" (9am), chief of the Crime Suppression Division Jirabhob Bhuridej told AFP.

Commandos from elite Thai police units killed the gunman, a police spokesman added, after an operation involving hundreds of security personnel.

"The official death toll is 20 and wounded 42... nine are in surgery," Narinrat Pitchayakamin, a Korat doctor told reporters, revising down an initial death toll of 21.

But it was unclear if there were more victims inside the multi-level complex which was packed with Saturday shoppers when the gunman stormed in.

A number of ambulances left the front of the complex and forensic police poured into the crime scene, shortly before the gunman's death was confirmed.

The night saw heavy exchanges of gunfire and evacuations.

National police chief Pol Gen Chakthip Chaijinda and Pol Lt Gen Poonsap Prasertsak, chief of the Provincial Police Region 3, confirmed on Sunday that the soldier was killed.

The shooter has been identified as Jakrapanth Thomma, 32, of the Surathampithak army camp.

Another source said Sgt Maj 1st Class Jakrapanth was killed near Foodland supermarket in the basement of the shopping centre.

A provincial public health official told a press conference on Sunday 20 people had been killed and 42 injured.

The figures excluded five others found hurt in the shopping centre on Sunday morning.

Volleys of gunfire rang out before dawn, hours after security services stormed the ground floor of Terminal 21 where the gunman had held out, armed with assault weapons stolen from his barracks, for more than 17 hours.

As police entered the mall, scores of stunned and terrified shoppers fled a bloody rampage that the gunman relayed via Facebook posts.

But it was unclear how many people remained inside the mall.

The latest casualty was a police officer who took part in a raid around 3am to force the gunman out.

Shocked evacuees recounted how an ordinary Saturday shopping day at the busy mall descended into horror as the gunman entered.

"It was like a dream... I'm grateful I survived," Sottiyanee Unchalee, 48, told AFP, explaining she hid in the toilet of a gym inside the mall as she heard the gunfire.

"I'm so sorry for those who died... (and) the people still trapped inside."

Automatic weapon fire rang out just before dawn as ambulances prepared to evacuate the wounded in an attack whose motives remain unclear.

Stolen weapons

As shoppers ran for the exits late Saturday, police urged evacuees to "raise their hands" and identify themselves on the ground floor over fears the gunmen could hide among the crowds.

Earlier, Sgt Maj 1st Class Jakrapanth relayed his shooting spree through Facebook posts which charted the attack from the army barracks in the city to the mall, where an unknown number of shoppers remained trapped.

A volunteer rescue worker recounted a bloody scene of horror after his team carried four corpses to the hospital.

"I've never seen anything like this," Peerapong Chatadee told AFP.

"I just feel so sad. He is a soldier, he should not have fired at unarmed people."

The bloodshed began Saturday afternoon when Sgt Maj 1st Class Jakrapanth shot three people -- among them at least one soldier -- at a senior officer's house and then at the nearby army barracks, before driving an army vehicle to the town centre.

There the gunman used weapons stolen from the military arsenal to unleash carnage in the town centre.

He "used a machine gun and shot innocent victims resulting in many injured and dead", said police spokesman Pol Krissana Pattanacharoen.

Throughout the day, Sgt Maj 1st Class Jakrapanth posted images of himself and wrote several posts on his Facebook page as the attack unfolded.

In one Facebook video -- since deleted -- the assailant, wearing an army helmet, filmed from an open-top jeep, saying, "I'm tired... I can't pull my finger anymore" as he made a trigger symbol with his hand.