UPDATE, 6:34 EST: The death toll from the fertilizer plant explosion in West, TX, has risen to about 35 people, including 10 first responders, according to West Mayor Tommy Muska.
* Three or four volunteer firefighters missing
* More than 160 people injured in disaster
* Police say five to 15 people killed
* As many as 80 homes damaged
Rescue workers searched the wreckage of a fertilizer plant on Thursday for survivors of a fiery explosion that killed as many as 15 people, injured more than 160 and leveled houses in a small Texas city.
Three to four volunteer firefighters were among the missing following the explosion on Wednesday night, said Sgt. William Patrick Swanton of the Waco, Texas, police department.
Firefighters had responded to a fire at the West Fertilizer Co before the 8 p.m. blast that rocked West, a town of 2,700 people about 20 miles (32 km) north of Waco.
The death toll remained estimated at five to 15 people, Swanton said at a news conference in Waco on Thursday. "That's a rough number," he said.
"There are still firefighters missing," Swanton said. "They were actively fighting the fire at the time the explosion occurred."
Rescuers are still in a "search and rescue" mode," he said.
"That's good news to me, meaning that they're probably still getting injured people," Swanton said. "They have not gotten to the point of no return where they don't think that there's anybody still alive."
A law enforcement official was found alive but in critical condition in a local hospital, Swanton said.
President Barack Obama, who flew to Boston for a memorial service for victims of the Boston Marathon bombing, offered support and prayers to the victims in Texas.
Witness Kevin Smith told CBS News he had just climbed the stairs to the second floor of his home when he felt the blast.
"The house exploded. It was just a bright flash and a roar, I thought it was lightning striking the house," Smith said. "I felt myself flying through the air about 10 feet, and it took a second or two to realize that the roof had caved in on me so I knew it wasn't lightning."
Light rain was falling and winds had picked up to 22 miles per hour (35 kph) Thursday morning, conditions that could complicate the recovery effort or prompt additional evacuations.
"I've never seen anything like this," McLennan County Sheriff Parnell McNamara said. "It looks like a war zone with all the debris."
Hillcrest Baptist Medical Center in Waco admitted 28 of more than 100 people it treated, with five in the intensive care unit, said David Argueta, vice president of operations.
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.
Ground motion from the blast, triggered by a fire of unknown origin at the plant, registered as a magnitude 2.1 seismic tremor and created a jolt felt 80 miles(130 km) away in Dallas, the U.S. Geological Survey reported.
The firefighters had been battling the fire and evacuating nearby houses and a nursing home for about 20 minutes before the explosion occurred.
Texas Public Safety Department spokesman D.L. Wilson said about half the town, eight to 10 blocks, had been evacuated and that "we might even have to evacuate on the other side of town" if winds shift.
Wilson said 50 to 75 houses were damaged by the explosion and fire, 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 were evacuated from the nursing home, which was heavily damaged, but it was not known how many residents had been hurt. A middle school also was badly damaged.
Three hospitals in Waco and Dallas reported treating more than 160 injuries from the blast.
"We are seeing a lot of lacerations and orthopedic-type injuries ... things you would expect in an explosion," said Argueta at Hillcrest Baptist.
Jason Shelton, 33, a father of two who lives less than a mile (1.6 km) 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 said 21 National Guard members had been sent to help with emergency response efforts.
Obama said federal emergency officials were monitoring the local and state response.
The U.S. Chemical Safety Board said it is sending a "large investigation team" to the scene.