The Texas EMS director believes that number will climb to as many as 70.

Reuters has the details:

A fiery explosion tore through a fertilizer plant and leveled dozens of homes in a small Texas town late on Wednesday, killing as many as 15 people, injuring more than 160 others and spewing toxic fumes that forced the evacuation of half the community, authorities said.

[...]

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

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 tremor 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 Reuters that five or six volunteer firefighters who were among the first to arrive at the fertilizer plant were missing.

While terrorism can't be ruled out, this wouldn't be the first fertilizer explosion in Texas history. Sixty six years ago, a French cargo ship being loaded with ammonium nitrate exploded in Texas City with far more force than the plant blast, killing at least 576 (no official tally was ever made) and leveling half the town.

Our thoughts should also be with the people of West, Texas today as they sift through the wreckage to find their loved ones.