WASHINGTON (REUTERS) - President Barack Obama issued an emergency declaration for Texas on Friday to help the state cope with the fallout from a deadly fertiliser plant explosion.

The order authorises the Federal Emergency Management Agency to "identify, mobilize, and provide at its discretion, equipment and resources necessary to alleviate the impacts of the emergency".

Wednesday's blast occurred at a fertiliser plant in the town of West, Texas, and killed at least 14 people, including volunteer firefighters who raced to the scene to douse a blaze.

Authorities said 200 people were injured.

There was no indication of foul play at the West Fertilizer Co plant, a privately owned retail facility.

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

"I want them to know that they are not forgotten," Mr Obama said in an appearance in the White House briefing room that focused on the capture of the surviving suspect in the Boston Marathon bombings.

"Our thoughts, our prayers, are with the people of West, Texas, where so many people lost their lives, some lost their homes, many are injured, many are still missing," Obama said.

"All in all, this has been a tough week."