Up to 70 people have been reported dead in a fertiliser plant explosion near Waco, Texas.

The Emergency Medical Services director in the town of West, Dr George Smith, told the local KWTX station as many as 60 or 70 people had died and hundreds were injured in the blast on Wednesday night.

A rescuer earlier said he knew of five deaths.

The town of 2700 people was being evacuated in school buses and ambulances because of ammonia fumes, CBS reported.

Gayle Scarbrough, a spokeswoman for the Department of Public Safety in Waco, told reporters that officers had transporting injured people to hospitals in their patrol cars. She says six helicopters were also en route. Emergency crews were called in from central and north Texas to help.

A triage stations set up at the local high school football field had to be moved because of an overpowering smell.

The blast at West Fertiliser plant was reported shortly before 8pm local time (11amAEST on Thursday).

Several buildings, some in residential areas, were reported to be burning, others destroyed, and a nearby nursing home was damaged, according to a report from a local broadcast station.

Initial reports said people were trapped in the nursing home and an apartment building.

Waco Assistant Fire Chief Don Yeager said the cause of the explosions was not immediately known.

Fire departments from nearby jurisdictions rushed to the scene where the blast was so powerful it knocked down some nearby buildings, and set fire to others, Mr Yeager said.

"An explosion has ignited adjacent structures to the plant," he said.


The United States was already on edge as it pieced through deadly explosions that hit the Boston Marathon on Monday, which were followed by letters, apparently poisoned with ricin, sent to a US senator and the US president, Barack Obama.

Friday will be the 20th anniversary of the Waco siege, a deadly confrontation between US authorities and heavily armed locals there. After a 51-day stand-off a gun battle broke out with US agents and the Branch Davidian compound burned. Dozens of people were killed in an incident that many far-right groups see as a symbol of egregious US government overreach.