WEST, Texas (AP) — Rescue workers searched rubble early Thursday for survivors of a fertilizer plant explosion in a small Texas town that killed as many as 15 people and injured more than 160 others. The blast left the factory a smoldering ruin and leveled homes and businesses for blocks in every direction. Waco Police Sgt. William Patrick Swanton said officials went building to building in the largely decimated area around the plant that exploded with the strength of a small earthquake in downtown West, a farming community about 20 miles north of Waco. "They have not gotten to the point of no return where they don't think that there's anybody still alive," Swanton said. He did not know how many people had been rescued. The explosion, which could be heard dozens of miles away, sent flames shooting into the night sky and rained burning embers and debris down on shocked and frightened residents. Swanton said earlier that authorities believe between five and 15 people were killed in the blast, but stressed it was an early estimate. There is no indication the blast was anything other than an industrial accident, he said. Three to five volunteer firefighters were among those believed to be dead, Swanton said. A single law enforcement officer who responded to a fire call at the West Fertilizer Co. shortly before the blast was accounted for early Thursday. The explosion that struck around 8 p.m. leveled a four-block area around the plant that a member of the city council, Al Vanek, said was "totally decimated." The toll included 50 to 75 houses, an apartment complex with about 50 units that one state police officer said was reduced to "a skeleton," a middle school and the West Rest Haven Nursing Home, from which first-responders evacuated 133 patients, some in wheelchairs.