A massive explosion at a fertiliser plant in Texas has devastated a town, levelling buildings, setting others on fire and causing casualties that authorities fear could run into the hundreds.

The blast shook the earth and rolled a huge fireball through the town of West at about 8pm local time on Wednesday, witnesses said, destroying homes and businesses.

"It was a like a nuclear bomb went off," the mayor, Tommy Muska, told reporters. "Big old mushroom cloud. There are a lot of people that got hurt. There are a lot of people that will not be here tomorrow."

Two people were immediately reported killed but the death toll could rise to 60 or 70, said George Smith, an emergency management system director. "That's a really rough number, I'm getting that figure from firefighters, we don't know yet." Firefighters were feared to be among the casualties.

Glenn Robinson, chief executive of Hillcrest Baptist Medical Centre in Waco, 18 miles south of the town, told CNN his hospital had treated 66 people, including 38 who were seriously hurt with blast injuries and lacerations.

David Argueta, vice-president of hospital operations, said staff had treated lacerations and orthopaedic-type injuries. "We are being told that we have seen most of the patients, and it's now turned into a search-and-rescue operation on scene."

A spokesman for the Texas department of public safety, DL Wilson, told Reuters the blast had probably caused "hundreds of casualties". A nursing home had collapsed and people were believed trapped inside, he said. It registered as an earth tremor of magnitude 2.1.

West, located in McLennan county in central Texas, is about 80 miles south of Dallas. It has a population of 2,700. The blast from its fertiliser plant was heard at least 45 miles away.

Television pictures showed apocalyptic scenes of fire and smoke from ruined buildings close to the factory.

There was no immediate confirmation on what caused the apparent accident, which followed a terrorist attack in Boston. US Representative Bill Flores, whose district includes West, told CNN he doubted foul play was involved. "I would not expect sabotage by any stretch of the imagination."