Three bomb attacks minutes apart killed nine people and wounded more than 100 on Saturday in the main town in Thailand's insurgency-hit far south, a hospital worker said.

The blasts hit the centre of Yala around midday as families were out shopping. Several shop houses near the blast sites were set on fire and many parked cars and motorcycles were damaged by the powerful explosions.

"There are nine dead now and 112 injured people sent to our hospital," a nurse in the emergency unit of Yala provincial hospital told AFP.

The public health ministry said 10 people were in critical condition with severe burns.

Colonel Pramote Promin, spokesman for the southern army region, earlier gave a toll of seven dead and more than 70 wounded.

"There were three bombs that exploded, the first is a car bomb and the second and third bombs were hidden in motorcycles," the colonel said.

A Yala city policeman added: "The bombs went off about 10 minutes apart."

Bomb squad officers were seen inspecting the mangled car wreckage at the site of the car bomb as firefighters doused blazes nearby.

Rescue workers helped bloodied victims and searched for other wounded people as smoke filled the street.

One policeman was wounded in a separate motorcycle bomb attack in Mae Lan district of neighbouring Pattani province, police said.

The Yala bombing was the worst attack since January last year, when nine people were killed by a bomb in a village in Yala province.

A complex insurgency, without clearly stated aims, has plagued Thailand's far south near the border with Malaysia since 2004, claiming thousands of lives, both Buddhist and Muslim, with near-daily bomb or gun attacks.

Struggling to quell the unrest, authorities have imposed emergency rule in the Muslim-majority region, which rights campaigners say effectively gives the army legal immunity.

The military last week admitted troops had shot dead four Muslim villagers on their way to a funeral due to a "misunderstanding" in late January after apparently fearing they were under attack from militants.

One of the region's deadliest incidents occurred on October 25, 2004, when seven people were shot dead as security forces broke up a protest in the town of Tak Bai, and 78 more suffocated or were crushed to death in trucks while being transported to a detention centre.

Rights groups have said the failure of Thai authorities to hold security forces to account over the deaths has fuelled further violence and alienation in the southern region.

The insurgents are not thought to be part of a global jihad movement but are instead rebelling against a long history of perceived discrimination against ethnic Malay Muslims by successive governments in the Buddhist-majority nation.