At least 12 people were injured in an explosion during an annual charity event in south Thailand, the Nation news agency reported on Monday.

The blast went off late on Sunday at a Red Crescent fair in a park in the southern province of Narathiwat's Mung District.

The bomb was hidden in a garbage bin near a stage where concerts were taking place, the agency said. The device is believed to have been detonated remotely with the use of a digital watch.

Up to four terrorist organizations are active in the south of Thailand. They are aiming to establish an independent Islamic state and are thought to have a combined total of several thousand fighters.