RESCUE teams were picking through the devastation in the small Texas town of West, near Waco, after a massive explosion at a fertiliser company flattened the surrounding neighbourhood.
Initial estimates put the death toll at between five and 15, with at least 160 injured.
Among the missing were three to four volunteer firefighters who were responding to a blaze at the facility when the explosion happened on Wednesday night.
Waco police Sergeant William Patrick Swanton said in a morning press conference that the emergency response was still in its search and rescue phase, but that eventually it would have to become one of recovery.
"They are still getting injured folks out and they are evacuating people from their homes," he said.
"They have not gotten to the point of no return where they don't think that there's anybody still alive."
The blast, which could be heard 45 miles away and shook the ground with a force equivalent to a magnitude 2.1 earthquake, levelling up to 80 homes in the blocks around the facility.
As a mushroom cloud climbed into the sky, more than 1,000 people in the town of around 2,800 were left without power.
An apartment complex was ripped to shreds, a middle school was reportedly in flames, and 133 people, many of them injured, were evacuated from a nursing home.
"I've never seen anything like this," said McLennan County Sheriff Parnell McNamara. "It looks like a war zone."
Emergency services said ammonia may have caused the fireball at West Fertilizer Inc, which reportedly had 20 tonnes of anhydrous ammonia on site.
The site was being treated as a crime scene, officials said, though in the immediate aftermath there was no indication of the blast being anything other than an industrial accident.
The fire at West Fertilizer, around 80 miles south of Dallas, reportedly began at around 6pm on Wednesday.
Local volunteer fire-fighters were battling the blaze and evacuating nearby homes as a precaution against toxic fumes when the ammonia exploded.
Jason Shelton, 33, a clerk at the Czech Best Western Hotel, told the Dallas Morning News: "It was a small fire and then water got sprayed on [it] and it exploded just like the Oklahoma City bomb… I live about a thousand feet from it and it blew my screen door off, and my back windows."
Debby Marak, 58, had just finished teaching a religion class when she spotted the smoke, and decided to drive across town to see what was going on.
When she got close to the plant, however, two boys came running towards her car, yelling that it was about to explode.
She turned the car around, but didn't get far before the blast engulfed her. "It was like being in a tornado," she told the Associated Press.
"Stuff was flying everywhere. It blew out my windshield."
Sergeant Swanton said that a residual burning underneath additional chemical tanks had been brought under control and no longer appeared to be a threat.
More than half the town had been evacuated, and Swanton revealed there had been reports of "a small amount of looting" in West following the fire, describing it as "a significant concern".
As the injured began to emerge from the blast zone on Thursday night, an emergency hospital was set up on a local sports field to treat patients with burns, shrapnel wounds and other injuries.
The local blood bank had queues of more than 200 people stretching around the block despite incessant rain, although there were fears that given the recommended interval between donations they would soon run short.
More than 100 of those injured in the explosion were taken to Hillcrest Baptist Medical Centre some 20 miles away in Waco. Today, 38 were said to be in a critical condition.
As the scale of the disaster became apparent, President Barack Obama, in Boston for a memorial service for victims of the Boston Marathon bombing, offered his prayers to the residents of West, saying, "They will have the support of the American people."
Texas state Governor Rick Perry said 21 National Guard members had been sent to assist the rescue effort. "Our thoughts and prayers are with the people of West, and the first responders on the scene," Perry said.
Today, it also emerged that the facility was cited in 2006 by the Texas Commission on Environmental Quality for failing to obtain or qualify for a permit, after a complaint of a strong smell of ammonia.
The authorities were also aware of the quantities of ammonia on site, despite its proximity to schools and the nursing home.
Nitrogen fertiliser a lethal mixture
For years farmers would struggle to get enough nitrogen fertiliser on to their fields. This changed after 1909 when discovered how to convert inert nitrogen gas in the atmosphere into ammonia. Now millions of tons are produced every year as fertiliser.
Anhydrous ammonia is a variant that is stored at temperatures above -33C, and is highly explosive if it mixes with air. Chemical plants contain it under high pressure in special tanks. The chemical itself is highly caustic, causing skin burns, eye irritation and lung damage.
Ammonium nitrate is the chemical constituent used to make explosives used mostly in the mining and demolition industry.
Eyewitness: 'There was a bright flash and a roar. I thought it was lightning'
As the tiny Texan town of West awoke, residents may have hoped their memories of the previous night had just been a terrible dream.
Instead, they were forced to begin coming to terms with the shock of the huge explosion at the West Fertiliser facility that has so far left up to 15 people dead and more than 160 injured.
"[My] house exploded," Kevin Smith told CBS News. "It was just a bright flash and a roar - I thought it was lightning striking the house … I felt myself flying through the air about 10 feet, and it took a second or two to realise that the roof had caved in on me so I knew it wasn't lightning."
Up to 70 homes and buildings were torn apart by the force of the blast, which was said to be the equivalent of a 2.1-magnitude earthquake.
Authorities said a nearby block of flats was reduced to little more than "a skeleton". Some 133 residents of a nursing home in the area were forced to evacuate, as toxic fumes from the site spread across the neighbourhood.
Another West resident, Julie Zahirniak, said she and her son, Anthony, had been playing at a school playground near the plant when it exploded. She said the blast threw Anthony four feet in the air, breaking his ribs.
"The fire was so high," she told the Associated Press. "It was just as loud as it could be. The ground and everything was shaking."
Erick Perez, 21, had been playing basketball close to West Fertiliser when the fire started. At first, he and his friends thought nothing of it. Around half an hour later, the blast threw him and his nephew on to the ground, and showered the area with hot embers, shrapnel and debris.
"The explosion was like nothing I've ever seen before," Mr Perez said. "This town is hurt really bad."
As emergency services continued their search-and-rescue operations in the hope of locating more survivors, residents who escaped the worst of the damage began attempting to clear up the mess created by the explosion.
"Nothing like this has ever happened," Mary Galvan told The Dallas Morning News. She was crying as she swept up broken glass from the pavement in front of the West Thrift Shop she manages - a small gesture towards what will inevitably be a long and painstaking process. "It is just terrifying," she said.
At a news conference, Texas Governor Rick Perry praised the emergency services and ordinary residents who rushed to help victims of the blast.
"Last night was truly a nightmare scenario for that community," Mr Perry said. "This tragedy has most likely hit every family and touched practically everyone in that town."