A car bomb has exploded at a shopping mall on the Thai island of Koh Samui, injuring at least seven people.

The improvised bomb was hidden in a pick-up truck and went off late on Friday night in the basement of the Central Festival mall on the resort island, Koh Samui's disaster prevention and mitigation chief Poonsak Sophonpathumrak said.

Poonsak said the bomb destroyed most of the truck and damaged a few other vehicles parked nearby at the mall, which is located a few hundred metres from the popular Chaweng beach.

"The authorities are still investigating the scene to find out more details before linking it to any insurgency groups,'' he said.

Poonsak said authorities believed the vehicle was stolen from one of the three southernmost Thai provinces, which have previously been the scene of unrest.

More than 5,000 people have been killed in the three southern provinces since 2004.

Car bombs have been used in attacks on other tourist destinations in southern provinces, but have never previously targeted Koh Samui.