Rescuers launched a door-to-door search Thursday for victims after a massive explosion at a Texas fertilizer factory killed as many as 15 people and leveled much of this small Texas town.
With the country already on edge from Boston Marathon attacks, the factory blew up in a huge fireball late Wednesday, destroying scores of nearby homes. Authorities said they feared they would find a lot more bodies in the rubble of homes and businesses leveled by the force of the blast.
Sergeant Patrick Swanton of the nearby Waco, Texas police department said that officials don't yet know caused the explosion, but are treating the site as a crime scene.
"We are not indicating that it is a crime, but we don't know," Swanton told US media overnight.
"What that means to us is that until we know that it is an industrial accident, we will work it as a crime scene," he said.
The main investigation was being led by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.
Swanton said the death toll is "anywhere from five to 15 at this point" but expected to rise. Hospitals have treated more than 160 people with varying injuries.
He said law enforcement and rescue officials were conducting a massive search for survivors.
"They are working together, to still find survivors, to still find people that are injured and are going door to door," he Swanton told reporters at a briefing.
"They are being very thorough, they are taking their time in their searches," he said.
The US Geological Survey recorded the force of the explosion at a 2.1 magnitude.
The blast, which was felt as many as 50 miles away, destroyed an apartment complex and a nursing home and sent residents fleeing into emergency shelters.
The acrid smell of smoke lingered in the air early Thursday. Authorities said that the fire was under control, but said there was no risk of another explosion.
President Barack Obama in a statement offered the prayers of the nation to the people of West.
"A tight-knit community has been shaken, and good, hard-working people have lost their lives," he said.
Obama offered aid through the Federal Emergency Management Administration, and promised "to make sure there are no unmet needs as search and rescue and response operations continue."
The explosion at the West Fertilizer Company came with the nation still raw with emotion after the Boston marathon bombings Monday, which left three people dead.
Americans also were on edge following a scare in which letters apparently laced with the poison ricin were sent to President Barack Obama and a US senator in Washington. Police arrested a suspect in that case late Wednesday.
Search and rescue efforts in West could be complicated by a storm system heading into the area, with forecasters predicting heavy rains, and winds possibly heavy enough to spawn tornadoes.
Swanton added that police another worry -- "a small amount of looting" that has broken out at unattended homes and businesses.
West, with a population of about 2,800 people, is home to a thriving Czech community dating back to the late 1800s, as immigrants settled the American frontier.
In Prague, the foreign ministry said its ambassador to Washington, Petr Gandalovic, was traveling to West to study the possibility of providing aid from his government for the injured and relatives of the victims.
The explosion came just ahead of the 20th anniversary on Friday of a deadly confrontation in Waco between federal authorities and heavily armed members of a religious group, the Branch Davidians, stoking worries about possible foul play.
The Federal Aviation Administration declared a no-fly zone over the area around West, over fears another blast could bring down small aircraft.
Witnesses said they were stunned by the sheer force of the blast.
"It knocked me down, it knocked me back. It was like the whole road just picked up," resident Cheryl Marich, whose home was destroyed and whose husband was fighting the blaze, told CNN.
Another witness, Bill Bohannan, told the Waco Tribune-Herald: "It knocked us into the car... Every house within about four blocks is blown apart."
In the 1993 Waco siege, following a 51-day standoff, the group's compound burned down after an assault was launched.
Dozens of people were killed in an incident that many far-right groups see as a symbol of egregious US government overreach.