Officials confirm up to 15 fatalities and more than 160 people injured after a blast at a Texas fertiliser plant near Waco, as Jonathan Miller reports.

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The blast, which came after a fire at the plant, was reported at about 8pm local time (1am GMT) north of Waco, Texas. Hours later, police warned that the situation was still volatile because of the presence of ammonium nitrate, an extremely hazardous material.

The initial estimate of five to 15 fatalities and over 160 people injured is expected to rise when emergency workers will be better able to assess the damage. Rescue workers are still searching for survivors.

The fertliser plant is now a crime scene, but Sergeant William Patrick Swanton from Texas police department said that this was normal practice and that there was no evidence to suggest the fire and subsequent explosion was not an accident.

"I will confirm there has been fatalities. I think we will see those fatalities increase," said Sergeant Swanton added.

"I can confirm that there may be firefighters unaccounted for and potentially a law enforcement officer as well. We are still trying to determine that."

Sergeant Swanton also said there had been a small amount of looting which was "a significant concern".

ABC News reported that hospitals near the blast were treating 179 people, with 10 more being triaged: at least 24 patients at the hospitals were in critical condition and 38 were in serious condition at 3.30am local time (8.30am GMT).

What could have caused the blast? Science Editor Tom Clarke reports:
It's being widely reported that tanks of anhydrous ammonia - a commonly used fertilizer - are the cause of the explosion at the plant in West, Texas. Anhydrous ammonia is a highly corrosive liquid that instantly turns into toxic ammonia gas, but on its own is not explosive.
The tanks of anhydrous ammonia at the West plant would have stored the liquid under high pressure. As a result of the fire, these tanks could rupture catastrophically causing a blast, says Prof Andrea Sella, a chemist at University College London.
However, video of the explosion, suggests the blast was much more violent than would be expected from a perssurised tank failing. "It looks to be a supersonic blast more likely to result from a detonation event," says Sella.
Another common type of fertiliser - ammonium nitrate - is notoriously explosive. It has caused some of the worst industrial accidents in history as well as being a favourite of home bomb makers. In 1947 a ship full of ammonium nitrate exploded in Texas City killing nearly 600 people.
According to environmental permits the West Fertilizer Company also stored nitric acid at the facility, which is used to make ammonium nitrate.

'Just like Iraq'

An estimated 50 to 75 homes were damaged by the explosion and a fire that followed, a spokesman for the Texas department of public safety, D.L. Wilson. A nearby 50-unit apartment complex had been reduced to "a skeleton standing up," he added.

A nursing home was also badly damaged in the blast and 133 people were evacuated, but it was not immediately clear how many of them were hurt and some residents may have been trapped inside.

"I walked through the blast area, I searched some houses earlier tonight. Massive - just like Iraq, just like the Murrah Building in Oklahoma City," he said.

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Devastation

The explosion happened in West, a town of around 2,700 people about 80 miles (130 km) south of Dallas and around 20 miles (32 km) north of Waco.

The air in town remained thick with smoke more than two hours after the explosion, and the area around the blast site was littered with shards of wood, bricks and glass.

There was no immediate official word on what sparked the explosion as emergency personnel assisted victims and doused the flames. US Representative Bill Flores, whose district includes West, said he doubted any foul play was involved.

West Texas Mayor Tommy Muska said they would make sure everyone was accounted for and asked people for their prayers. "There's a lot of people that got hurt. There's a lot of people that I'm sure are not going to be here tomorrow," he said.

"This is probably the major, most devastating thing that has happened to this community. But we're going to build back. It's not the end of the world, it's just a big old cut that we got across our hearts. So, we're going to search for everybody. We're going to make sure everyone is accounted for. That's the most important thing right now."

He also put the number of destroyed homes at between 60 and 80.

Hillcrest Baptist Medical Center in Waco reported treating 66 patients, including children, for injuries including lacerations, burns and broken bones.

A White House official said the Obama administration was aware of the situation and monitoring local and state response through the Federal Emergency Management Agency.

The explosion came two days before the 20th anniversary of a fire in Waco that engulfed a compound inhabited by David Koresh and his followers in the Branch Davidian sect, ending a siege by federal agents.