Four people are now known to have died in a series of bomb blasts in southern Thailand's commercial hub, Hat Yai.
A Canadian tourist was among those killed in Saturday evening's bombings, becoming the first Westerner to be killed by the separatist insurgency.
About 70 other people were injured in the blasts, several of them foreigners.
The blasts were the latest in a string of violent incidents in the restive south, where more than 1,500 people have been killed since January 2004.
Officials blame Muslim insurgents for much of the unrest, although criminal gangs are also thought to be behind some of the attacks.
Thai media reported that the bombs were hidden in motorcycles and triggered by mobile phones.
Most of the six bombs were placed near department stores and restaurants. Television pictures showed the Odeon and Big C department stores on fire.
The authorities had tightened security in the south over the weekend, fearing attacks to coincide with the anniversary of the foundation of one of the separatist groups there, the Gerakan Mujahideen Pattani (GMP).