The death toll from a fireworks explosion at a warehouse in Narathiwat on Saturday is now 12, with 121 injured and 292 houses damaged or totally destroyed.

Of the 121 injured, 111 had returned home. Ten were admitted to Sungai Kolok Hospital for treatment, with one in a serious condition.

Narathiwat's governor said the place was initally opened as a grocery shop. The owner then obtained permission to expand it to become a warehouse. It was believed to have been used to store fireworks without permission.

The explosion was believed to have been caused by sparks from a nearby welding shop.

The blast from around 1,000 kilogrammes of gunpowder caused two holes roughly two metres deep and six metres wide.

Most of the residents nearby were unaware fireworks had been stored in the warehouse. The building doors had been closed most of the time.

The huge blast damaged 292 houses nearby, totally destroying 50 of them.

A rescue worker in Sungai Kolok said when he led about 40 rescuers to the scene they saw only houses and shops ablaze with debris scattered over a wide area. Heavy equipment was used to break open the damaged houses to bring out the killed and injured.

Eyewitnesses reported a huge boom and the earth shaking on Saturday.

"I was playing with my phone inside the house then suddenly I heard a loud, thunderous noise and my whole house shook," eyewitness Seksan Taesen, who lives 100 metres away from the warehouse, said.

"Then I saw my roof was wide open. I looked outside and I saw houses collapsing and people lying on the ground everywhere. It was chaos."