A Thai soldier has killed 20 people and injured dozens more in a gun rampage in the city of Nakhon Ratchasima.
According to media, Jakraphanth Thomma, a junior officer, killed his commanding officer before stealing weapons from a military camp on February 8.
The suspect then continued his attack in a shopping centre, where he is now believed to be holed up.
Jakraphanth Thomma also posted about the attack on social media.
His motives remain unclear.
Thaim authorities have sealed off the Terminal 21 shopping center in Nakhon Ratchasima, also known as Korat, as they try to track down the suspect.
Troops and police have entered the building and there have been reports of more gunshots.
Defense ministry spokesman Lt. Gen. Kongcheep Tantravanich said hundreds of people had been brought out of the complex safely, but there could be dozens still in the building.
A tweet from security forces said the ground floor had now been cleared.
The Bangkok Post reported earlier that the suspect, who it said was 32 years old, had taken hostages, but this has not been officially confirmed.
Jakraphanth Thomma’s mother has been brought to the shopping center to try to persuade him to give himself up.
Public Health Minister Anutin Charnvirakul confirmed that 16 people had died at the scene of the shootings, with another four dying later in hospital. A total of 31 people have been injured, with 10 of them in a critical condition. But there are fears the numbers could rise.
The shooting began at about 15:30 local time at the Suatham Phithak military camp, where the commanding officer, named by the Bangkok Post as Col Anantharot Krasae, was killed.
According to the publication, a 63-year-old woman and another soldier were also killed there.
The suspect seized arms and ammunition from the camp before taking a Humvee-type vehicle.
Jakraphanth Thomma then opened fire at a number of sites before arriving at the Terminal 21 shopping center.
Local media footage appears to show the suspect getting out of his vehicle and firing shots as people flee.
CCTV footage shows him inside the shopping center with a raised rifle.
PM Prayuth Chan-ocha is following developments and expressed condolences to the families of those killed, a spokeswoman said.
The public health minister has put out an appeal for people to donate blood at hospitals in the area.
Jakraphanth Thomma posted on his social media accounts during the attack, with one post on Facebook asking whether he should surrender.
He had earlier posted an image of a pistol with three sets of bullets, along with the words “it is time to get excited” and “nobody can avoid death”.
Facebook has now taken the page down.
The social media platform said: “Our hearts go out to the victims, their families and the community affected by this tragedy in Thailand. There is no place on Facebook for people who commit this kind of atrocity, nor do we allow people to praise or support this attack.”