Rescuers searched on Thursday for survivors in the rubble of homes destroyed by a fiery fertilizer plant explosion in a rural Texas town that the mayor said had killed at least 14 people.

Among the dead are four paramedics killed in the chemical blast at West Fertilizer Co. on Wednesday evening after emergency responders rushed to put out a fire at the plant, West Mayor Tommy Muska said.

He said five volunteer firefighters are listed as missing and feared dead. The cause of the explosion, which injured more than 160 people, was not known and officials said no evidence of foul play had been found.

"All of that unknown ... is really scary, we don't know what has happened, who is alive, who is hurt, that's probably the worst part now," said Pat Lee, whose 92-year-old mother was injured in the blast on Wednesday evening.

Police initially put the death toll at up to 15, but later on Thursday Texas Department of Public Safety spokesman Jason Reyes told reporters that while the explosion had been deadly, it is not yet known exactly how many had been killed.

The Texas blast happened within days of the deadly Boston marathon bombings and the discovery of poisonous packages sent to President Barack Obama and a Republican senator - both incidents that revived memories of the September 11, 2001, attacks.

Agents with the U.S. Chemical Safety Board, a federal agency that investigates industrial chemical accidents, and the Bureau of Alcohol, Tobacco, Firearms and Explosives are on the scene of the blast, which was the strength of a magnitude 2.1 earthquake, according to the U.S. Geological Survey.

Firefighters had been battling a fire at the plant on Wednesday night for about 20 minutes before the blast rocked the town of 2,700 people about 20 miles north of Waco.

Texas Attorney General Greg Abbott toured the devastated area on Thursday and compared the scene to "a bombing site, the kind you see in Baghdad." He said authorities were combing the area "inch by inch."

The blast destroyed 60 to 80 houses, reduced a 50-unit apartment complex to what one local official called "a skeleton standing up" and left a horrific landscape of burned-out buildings and blackened rubble.

The flag at the West Volunteer Fire Department was flying at half-staff and chaplains were on site to console people. Muska said five firefighters in the 29-member department were injured.

Bryan Anderson, 41, injured along with his 9-year-old son Kaden near their home, said: "This doesn't happen in West, Texas. We are just a little town."

West has a strong Czech heritage, and the Czech Republic Embassy in Washington said on its website the ambassador was traveling to the town, which is known among Texans as the place to stop on the highway between Dallas and Austin for kolaches, a popular Czech pastry.

'Very volatile situation'

Police said the fertilizer plant was in a highly populated neighborhood. "It is still a very volatile situation," said Chief Deputy Sheriff Matt Cawthon of McLennan County.

West Fertilizer Co is a retail facility that blends fertilizer and sells it to farmers. It stored 270 tons of ammonium nitrate, along with other "extremely hazardous" chemicals including anhydrous ammonia in 2012, according to a report the company filed with the state government.

Anhydrous ammonia is used by farmers as fertilizer to boost soil nitrogen levels and improve crop production.

According to the Centers for Disease Control, mixing anhydrous ammonia and water produces a poisonous cloud. When ammonia mixes with air, it forms an explosive mixture, and containers may explode when heated, according to the CDC.

The West plant is one of thousands of sites across rural America that store and sell hazardous materials such as chemicals and fertilizer for agricultural use, many within close range of residences and schools. The company is privately owned and has fewer than 10 employees.

The plant had not been inspected by state officials since 2006, when a complaint of an ammonia smell was resolved, said Zak Covar, executive director of the Texas Commission on Environmental Quality. State inspections are done only when there is a complaint, Covar said.

The federal Environmental Protection Agency fined the firm $2,300 in 2006 for failing to implement a risk management plan.

The plant's owner could not be reached for comment.

Firefighters had been evacuating several blocks around the fire before the blast out of concern for dangerous fumes, police said. That threat had abated by Thursday, police said.

The West middle school, which was badly damaged, was one fifth of a mile from the plant and the high school was one-third of a mile away.

Texas Governor Rick Perry declared McLennan County a disaster area and said he would request federal disaster aid from Obama. The president, who flew to Boston for a memorial service for victims of the Boston bombings, offered support and prayers to the victims in Texas.

Texas is no stranger to industrial disasters. In 1947, 3,200 tons of ammonium nitrate fertilizer detonated aboard a ship in a Texas City port, killing almost 600 people, an incident believed to be the deadliest industrial accident in U.S. history.

More recently, a 2005 explosion at a BP refinery in Texas City killed 15 people and injured more than 170 others when hydrocarbon vapors exploded in a processing plant.

If the West blast was an industrial accident, investigators would look at whether firefighters ignited the blast by pouring water on a volatile substance. Nim Kidd, chief of the Texas Division of Emergency Management, said it was too early to speculate.

"A lot of firefighters will use their No. 1 tool, which is water, in a hazardous materials chemical situation to cool the surrounding environment," he told a briefing in Austin.