Footage shows the aftermath of a grenade attack at a music festival in Thailand that killed three revellers and injured dozens more.

The explosive device was hurled into a crowd of concert-goers dancing in front of the stage in Tak province on Friday night shortly before 11:30 pm local time.

Police said that two people were killed at the scene and a third died later in hospital. At least 48 others were injured, many of them seriously.

Footage captured in the moments after the explosion shows bodies scattered along the ground. Some of the victims were receiving treatment and others were being helped to their feet at the Red Cross fair in the Umphang district, close to the border of restive Myanmar.

Witnesses said that they saw a group of young men acting suspiciously before the explosive device was thrown.

Officers later arrested two teenagers, aged 16 and 17, who were allegedly behind the attack. They have both been remanded in custody while investigations continue.

Police Lieutenant General Archayon Kraithong, spokesman for the Royal Thai Police Office, said the suspects were being grilled to find out whether it was an isolated attack or connected to a terror network.

Prime Minister Paetongtarn Shinawatra, who was in Hua Hin, offered her condolences to the families of the victims.

Paetongtarn, the daughter of former PM and ex-Man City owner Taksin Shinawatra, said she has ordered the Royal Thai Police and security agencies to investigate the attack, track down the perpetrators and take care of the injured and families of those killed.

The PM also instructed the police to increase security at all festive event venues during the holiday season.