Up to 15 people are thought to have been killed and more than 160 injured after a massive explosion and fire tore through a fertiliser plant and razed dozens of homes in a small Texas town on Wednesday night.

Authorities in the town of West, north of Waco, said the blast site was being treated as a crime scene, although they stressed they had no evidence of foul play.

The blast shook the earth and rolled a huge fireball through the town at about 8pm local time, raining burning debris and shrapnel over a five-block radius.

Sergeant William Patrick Swanton of Waco police, who said the death toll was only an estimate as search and rescue operations were still taking place, added there was nothing to suggest the blast was anything other than an industrial accident.

The McLennan county sheriff, Parnell McNamara, said: "I've never seen anything like this. It looks like a war zone with all the debris."

The mayor of West, Tommy Muska, said it was as if a nuclear bomb had been detonated: "Big old mushroom cloud. There are a lot of people that got hurt. There are a lot of people that will not be here tomorrow."

Remains of the fertiliser plant and other buildings and vehicles. Photograph: EPA

Muska told Reuters that five or six volunteer firefighters who were among the first on the scene were missing. They had been battling the fire and evacuating nearby residences and a nursing home for about 50 minutes before the blast occurred.

Police estimate that between five and 15 people have been killed, adding that more than 160 are being treated for their injuries at the local hospital as well as at Waco, 18 miles away, and Dallas, 80 miles away.

Units from 30 fire departments brought the blaze at the West Fertiliser Company plant under control by midnight. Fears that a second fertiliser tank might explode receded but authorities continued to evacuate residents amid concern about toxic fumes.

David Argueta, vice-president of operations at Waco's Hillcrest Baptist medical centre, said staff had treated lacerations and orthopaedic-type injuries. "We are being told that we have seen most of the patients, and it's now turned into a search-and-rescue operation on scene," he said.

A spokesman for the Texas department of public safety said a nursing home had collapsed and people were believed trapped inside.

West, located in McLennan county in central Texas, has a population of 2,800. The blast registered as a 2.1-magnitude seismic event and was heard at least 45 miles away. Television pictures showed apocalyptic scenes of fire and smoke from ruined buildings close to the factory.

There was no immediate confirmation on what caused the incident, which followed a bomb attack in Boston, but the US representative Bill Flores, whose district includes West, ruled out foul play. "I would not expect sabotage by any stretch of the imagination," he told CNN.

A fire at the factory reportedly started at about 6pm. Firefighters and police were tackling the blaze and evacuating residents when the explosion – its fireball captured in dramatic video footage – erupted at about 7pm. Several firefighters and at least one police officer were reported missing.

A teacher, Debby Marak, 58, told Associated Press that after teaching a religion class she noticed plumes of smoke coming from the area across town near the plant, which is near the nursing home. When she drove over to investigate two boys ran towards her screaming that authorities told them to leave because the plant was going to explode. She said she drove about a block before the blast struck. "It was like being in a tornado. Stuff was flying everywhere. It blew out my windshield. It was like the whole earth shook," Marak said.

Her husband, who was in another part of town when the blast hit, told her a huge fireball rose like "a mushroom cloud".

Locals receive medical treatment after the blast. Photograph: Rod Aydelotte/AP

Hours later, TV helicopters showed fires still smouldering in the factory and nearby buildings, including what appeared to be a school.

Firefighters expressed concern about anhydrous ammonia, a gas used in fertiliser that can poison and cause severe burns. State troopers in gas masks set up roadblocks and directed traffic away from the scene.

The Red Cross was working with emergency management officials in West to shelter displaced and evacuated residents.

Lydia Zimmerman told the KWTX station that she, her husband and daughter were in their garden in Bynum, 13 miles from West, when they heard multiple blasts. "It sounded like three bombs going off very close to us," she said.

The explosion came two days before the 20th anniversary of a conflagration in Waco when federal agents ended a siege by storming the compound of David Koresh and his Branch Davidian sect followers, resulting in the deaths of 82 members of the sect and four federal agents.