Dozens of people were still unaccounted for after investigators sifted through debris to pinpoint the cause of a fertiliser plant explosion at a tiny Texas farm town that killed at least 14 people and injured 200.

President Barack Obama on Saturday promised to commit resources to help the people affected by the explosion on Wednesday at West Fertilizer Company, 130km south of Dallas.

Police said there was no indication of foul play in the fire or the blast it triggered at the privately owned farm supply business that was last inspected two years ago.

The plant had notified a state agency that it stored potentially combustible ammonium nitrate on the site.

Mayor Tommy Muska said that the confirmed death toll was at 14 after remains were recovered from the area.

Powerful as earthquake

US Senator John Cornyn of Texas said the town's deputy fire marshal told him that 60 people remained unaccounted for.

He said that number was expected to drop, however, as people turned up at hospitals or with relatives and others, some of them outside of town.

"I would just take that with a grain of caution," Cornyn said.

Most of the confirmed dead were emergency personnel who responded to a fire and were likely killed by the ensuing blast, which was so powerful it registered as a magnitude 2.1 earthquake.

It ravaged a 50-unit apartment complex, demolished about 50 houses and battered a nursing home and schools.

Officials said the ruins of nearly 175 homes and other buildings left badly damaged or destroyed had been searched and "cleared" as of Friday afternoon as rescue teams combed wrecked structures for people who might have been trapped.

Governor Rick Perry said after touring the scene on Friday that he was advised that the search and rescue phase was

complete.

Asked whether that meant no more survivors were expected to be found, he said he did not know enough to comment.

'Not forgotten'

The precise origins of the disaster remained a mystery as agents from the US Bureau of Alcohol, Tobacco, Firearms and Explosives began investigating the blast site on Friday to collect debris and other evidence that may point to a cause.

Obama issued an emergency declaration for Texas on Friday that authorised the Federal Emergency Management Agency to mobilise any resources it needed necessary to help the state cope with the aftermath of the plant blast.

West has held a memorial service for blast victims [Reuters]

"I want them to know that they are not forgotten," Obama said in an appearance in the White House briefing room.

Authorities said they were treating the blast site as a crime scene but they strongly suspected it was an industrial accident.

Every one of the town of 2,800 residents seemed to know someone who had died or was presumed dead.



Brian Uptmor, 37, said his brother disappeared after he went to save horses in a pasture near the plant.

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

"He is dead," his brother said. "We don't know where his body is. It'll probably hit me at the funeral."

Hundreds of mourners in the town, known for its ethnic Czech heritage, packed St Mary's Catholic Church of the Assumption for a memorial service on Friday night.

Surviving members of the volunteer fire department, all dressed in red T-shirts, left the service together in a grim procession and gathered outside around one of their fire trucks.