At least 50 people have been injured after a double explosion at a busy shopping centre in southern Thailand, according to military reports.

A suspected car bomb was detonated at the entrance to the Big-C shopping centre in downtown Pattani, a province that has suffered waves of secessionist violence since 2004.

A first bomb was detonated inside the building, followed by a second explosion outside the centre, which targeted shoppers running from the first blast. The military had earlier said the initial blast was firecrackers.

​Images on social media show widespread destruction from the explosions, with smoke billowing from the centre and debris scattered around its entrance and car park.

No deaths have been reported, according to a military spokesperson, however two of the wounded were said to be in a critical condition.

The explosions appeared to be the latest attack by Muslim separatists in the south of the predominantly Buddhist country.

A decades-old separatist insurgency in the largely ethnic Malay Muslim provinces of Yala, Pattani and Narathiwat has killed more than 6,500 people since 2004, according to independent monitoring group Deep South Watch.

Attacks in Thailand's deep south have intensified this year.