Thai police said on Saturday that at least 17 people had been killed when a soldier went on a shooting rampage in the northeastern city of Nakhon Ratchasima.
Police spokesman Kissana Phathanacharoen told reporters that more than 20 others had been wounded.
The solider reportedly opened fire at a shopping mall following a dispute. Video taken outside the mall and shared on social media showed people taking cover in a parking lot as gunshots were fired.
Authorities said that the suspect was still inside the building and they were trying to apprehend him as the area surrounding the mall remained under lockdown. They added that the man was stationed at an army base outside of the city, and initially shot dead a fellow soldier and a woman.
"As for the motive to the incident, we have to wait for officials to catch him and interrogate him first," military commander Lieutenant General Thanya Kiatsarn said in a statement.
Police officers cited by the Associated Press news agency said the man took a gun and military vehicle from his base before driving to the mall, opening fire along the way.
DW's correspondent in Thailand, Florian Nusch, said the Health Minister was encouraging people in the local region to go to hospitals to donate blood.
Prime Minister Prayuth Chan-ocha expressed condolences to the families of those killed.
Suspect posted messages on social media
The suspect, identified by the Thai Defense Ministry as Sgt. Jakrapanth Thomma, posted messages on his Facebook page during his alleged rampage, writing "No one can escape death" and "Should I give up?"
Facebook later said that it had removed the account and would "work around the clock to remove any violating content related to this attack as soon as we become aware of it."
Read more: Facebook to tighten livestream access after Christchurch attacks
"Our hearts go out to the victims, their families and the community affected by this tragedy," a Facebook representative said in a statement. "There is no place on Facebook for people who commit this kind of atrocity."
While it is legal to own firearms in Thailand, mass shootings there are unusual.
"Thailand is among the leading nations when it comes to private gun ownership, so (there are) a lot of guns in this country," DW's Florian Nusch said. "Someone who actually goes on a rampage, who posts his actions online, who targets (people) indiscriminately — this is something very very rare here in Thailand."
Nakhon Ratchasima lies around 250 kilometers (155 miles) northeast of the Thai capital, Bangkok.
nm,es/rc (AP, AFP, Reuters)
Every evening, DW sends out a selection of the day's news and features. Sign up here.