Daniel Walker: Search for Survivors After Explosion in Texas Factory Kills at Least 5.

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 n 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 what caused the explosion, but they are treating the site as a crime scene. We are not indicating that this 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 wit 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, 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, and 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 lace with the poison ricin were sent to President Barack Obama, and a US senator in Washington.