Investigators are searching for clues to the cause of an explosion and inferno after an apparent industrial accident at a Texas fertiliser plant flattened sections of a small town and killed at least 12 people.

Authorities said there was no indication of foul play in the blast at West Fertilizer Co, which they said had not been inspected since 2006. The plant was storing potentially combustible ammonium nitrate and was located in a residential area.

A Texas state official said yesterday 12 people died in the blast and approximately 200 were injured. Earlier, the town's mayor said 14 had died.

The deaths included paramedics and volunteer firefighters who rushed to put out an initial fire and were engulfed by the ensuing blast, which was so forceful it registered as a magnitude 2.1 earthquake.

It left a devastated landscape, reducing a 50-unit apartment complex to what one local official called "a skeleton standing up," destroying 60 to 80 houses and heavily damaging a nursing home and schools.

Everywhere in the town of 2700, shocked residents mourned the loss of family and friends.

Brian Uptmor, 37 said his brother disappeared after he went toward the fire on Wednesday night to try to save some horses.

William "Buck" Uptmor, 44, has not been found among the estimated 160 injured at area hospitals, and has not answered his mobile phone.

"He is dead. We don't know where his body is," said Mr Uptmor, a former firefighter.

Residents gathered at the Out West Bar and Grill in downtown West on Thursday night, where some of the first responders who died in the blast used to drink.

"Everyone's still shocked," said 48-year-old Kenny Chudej, who listed the names of several people he said he knew had died.

"We lost a lot of good friends. I don't think it has hit home yet."

West Mayor Tommy Muska had earlier said four paramedics were among the known dead and five volunteer firefighters were listed as missing.

The West plant is one of thousands of sites across rural America that store and sell hazardous materials.

The plant had not been inspected by state officials since 2006, when a complaint of an ammonia smell was resolved. The federal Environmental Protection Agency fined the firm $2300 for failing to implement a risk management plan.