The death toll from a mass shooting in Thailand on Thursday climbed to 35, most of whom are children, state media reported.

A gunman opened fire at a childcare center in the upper northeastern province of Nong Bua Lam Phu, killing at least 35 people, 24 of whom were children, Thai public broadcaster PBS News reported.

It added that 12 others were injured and are being treated.

The shooter used a gun and knife to attack the childcare center.

After the attack, he killed his wife and their child before committing suicide.

He is said to be a 34-year-old former police officer.