The Muslim-majority border region has seethed with violence for over a decade as ethnic Malay insurgents battle the state.
The Muslim-majority border region has seethed with violence for over a decade as ethnic Malay insurgents battle the Buddhist-majority state for more autonomy.
The latest attack hit the town of Pattani around 2pm with two bombs going off outside the Big C, a busy supermarket near the town centre.
The first device was packed inside a motorcycle in the car park, officers said, spreading panic among shoppers.
"The second blast was a car bomb," Pattani police commander Major General Thanongsak Wangsupa told AFP.
Deputy national police spokesman Krissana Pattanacharoen told reporters 51 people were injured by the blasts, four of them seriously.
Video posted by a witness on Twitter showed the second blast detonate in a large fireball, sending bystanders running for cover.
Police were on the scene and appeared to be encouraging people to move back when the second blast struck.
In heavy rain forensic officers started searching through the twisted remains of the car looking for clues, an AFP photographer said.
A large swathe of the supermarket storefront had been blown away, replaced by a twisted mess of charred metal.
"I heard a very loud explosion," a resident who lives close to the supermarket told AFP, requesting anonymity.
"Minutes after that, I heard the sirens of rescue cars and ambulances. I feel bad about it... it happened at a place where people go to buy things."
Near-daily shootings and bomb attacks have claimed more than 6,800 lives since 2004, with both sides accused of rights abuses.
The simmering insurgency plays out far from Thailand's popular tourist resorts and receives little international attention as a result.
The UN children's agency condemned those behind the blasts for targeting an area where youngsters would be present.
"No child's life should ever be put at risk in this way. This is wholly unacceptable," said UNICEF's Thailand representative Thomas Davin.
Talks between the Thai junta and an umbrella group claiming to represent the rebel foot-soldiers have staggered along for years without any result.
Thai negotiators do not believe their rebel interlocutors have the power to stop the violence.
The rebels want peace talks to include international observers, as well as discussions on devolving political power and on protecting their Malay-Muslim culture.
But shortly before Tuesday's attack junta chief Prayut Chan-O-Cha reiterated his opposition to foreign involvement in solving the festering conflict.
"We must keep this issue away from the reach of the international arena," he told reporters in Bangkok.