Barely two days after the explosion in the Boston Marathon another fiery explosion has torn through a fertilizer plant and leveled dozens of homes in a small town in Texas, U.S

The explosion occurring shortly before 8 p.m. local time on Wednesday has killed as many as 15 people, injuring more than 160 others and spewing toxic fumes that forced the evacuation of half the community, authorities said.

Police initially estimated that between five and 15 people had perished in the blast, which rocked the town of south of Dallas,

Public safety officials said they expected the death toll to climb as search teams combed through the rubble of the demolished plant and surrounding homes.

"I've never seen anything like this," McLennan County Sheriff Parnell McNamara said. "It looks like a war zone with all the debris."

Ground motion from the blast, triggered by a fire of unknown origin at the West Fertilizer Co plant, registered as a magnitude 2.1 seismic tremors and created a jolt felt in Dallas and beyond, the U.S. Geological Survey reported.

Waco Police Sergeant W. Patrick Swanton said investigators would examine whether the blaze was the result of foul play or a chemical reaction, adding that the blast site was being treated as a crime scene for the time being.

"We are not indicating that it is a crime, but we don't know," Swanton told reporters early on Thursday, some nine hours after the blast. "What that means to us is that until we know it is an industrial accident, we will work it as a crime scene." He said there was no immediate evidence of a crime.

The explosion came two days before the 20th anniversary of a fire in nearby Waco that engulfed a compound inhabited by David Koresh and his followers in the Branch Davidian sect, ending a siege by federal agents.

About 82 members of the sect and four federal agents died at Waco.

West Mayor Tommy Muska told journalists that five or six volunteer firefighters who were among the first to arrive at the fertilizer plant were missing.

Firefighters had been battling the fire and evacuating nearby residences and a nursing home for about 20 minutes before the explosion occurred.

Officials said flames that continued to smolder inside the plant initially posed two threats: the possibility of setting off further explosions and the emission of hazardous fumes into the town.

Swanton said a residual fire burning underneath additional chemical tanks had been brought under control, "and I don't think that is any longer a threat."

Texas Public Safety Department spokesman D.L. Wilson said about half the town, about eight to 10 blocks, had been evacuated and that "we might even have to evacuate on the other side of town" if winds shift.

But emergency management personnel downtown determined that there was no immediate danger to the public from the smoke from the fire, Swanton said.

Officials said a full assessment of property damage would not come until after dawn.

Wilson said 50 to 75 homes were damaged by the explosion and a fire that followed, and a nearby 50-unit apartment complex had been reduced to "a skeleton standing up." Muska put the number of destroyed homes at between 60 and 80.

Wilson said 133 people had been evacuated from the nursing home, which was heavily damaged, but it was not immediately clear how many residents of the facility were hurt. A middle school in town also was heavily damaged.

Three hospitals in Waco and Dallas that were receiving the bulk of patients from the disaster reported treating more than 160 injuries combined.

"We are seeing a lot of lacerations and orthopedic-type injuries ... things you would expect in an explosion," said David Argueta, vice president of operations at Hillcrest Baptist Medical Center in Waco.

Jason Shelton, 33, a father of two who lives less than a mile from the plant, said he heard fire trucks heading toward the facility five minutes before the explosion and felt the blast as he stood on his front porch.

"My windows started rattling and my kids screaming," Shelton said. "The screen door hit me in the forehead ... and all the screens blew off my windows."

Governor Rick Perry issued a statement saying his office had "mobilized state resources to help local authorities" deal with the incident.

A White House official said the Obama administration was aware of the situation and monitoring local and state response through the Federal Emergency Management Agency.