A second explosion took place 10 metres away from the venue but no one was harmed.
Police and bomb squad officers checked the scene yesterday and agreed that the two bombs were set to detonate 15 minutes apart, with the second aimed at responding officials.
A security source said the attack was part of unrest in the South and carried out by insurgents; Seri Waemanu and Ibrohim Samae, who have been active in Songkhla and Pattani.
The attack prompted security officers to raise their alert to the highest level in Hat Yai, with security teams on guard for suspicious vehicles and focusing on 32 areas designated as possible targets.