Image caption Police say there is no reason to believe the blast was not an accident

The number of people killed in an explosion at a US fertiliser plant has risen from 12 to 14, after officials recovered two more bodies.

Another 200 people were reportedly hurt in the blast in the state of Texas.

Texas US Senator John Cornyn said some 60 people were thought to still be missing, but stressed the number was expected to come down as search and rescue efforts continued.

The blast destroyed dozens of buildings in the town of West, near Waco.

Earlier, the town's mayor said he believed four firefighters who attended the original fire were among the dead, though this has not been confirmed.

Investigators were still looking for clues as to what may have caused the blast, officials said on Friday.

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'Terrible tragedy'

Officials confirmed they had recovered two more bodies on Friday, raising the death toll from 12 to 14.

Jason Reyes of the Texas Department of Public Safety said search and rescue efforts were still ongoing.

Meanwhile Senator Cornyn said local authorities had told him that some 60 people remained unaccounted for in this "terrible tragedy".

But he warned "to take that with a grain of caution" as many of the missing may be in hospital, staying with friends or relatives, or may have left town.

There was no indication that the blast and a fire which preceded it were anything other than industrial accidents, according to police.

However, they said that the site was being treated as a crime scene.

The explosion produced a tremor similar to a small earthquake.

A resident near the plant told the AFP news agency his home had sustained major damage in the explosion.

"I saw the house, it's in bad shape," he was quoted as saying.

"The door is blown in, windows are blown in. All of the ceiling has collapsed on to the floor."

Texas Governor Rick Perry earlier said he was declaring the area a disaster and would request an emergency declaration for federal aid from President Barack Obama, who has offered any help needed.

Air quality and gas pipelines are being monitored for safety, and gas supplies have also been disconnected until any risk has passed.

Emergency services officials earlier said the explosion might have been caused by the chemical ammonia.

The explosion devastated the West Fertilizer Company, about 20 miles (32km) north of Waco, in central Texas.

Dozens of homes were levelled and other buildings - including a school and nursing home a few hundred metres from the plant - were badly damaged.