At least 14 people have been killed and dozens injured in the explosion of a freight train carrying gas which derailed in northern Italy.
The carriages jumped the tracks and crashed into homes in the seaside town of Viareggio on Monday night.
Several of the victims died when their houses collapsed.
Firefighters are searching for people believed to be trapped. An investigation into the causes of the crash is under way.
The area is still at a really high risk level because the fire is still smouldering
Guido Bertolaso Civil Protection Department
Local officials initially gave the death toll as 16, but the figure was revised later on Tuesday.
However, Prime Minister Silvio Berlusconi told a news conference that four people were still missing and the toll could rise.
Guido Bertolaso, head of Italy's civil protection agency, said 13 wagons, each carrying a tank of liquefied petroleum gas, were still lying on or by the tracks.
"The area is still at a really high risk level because the fire is still smouldering," he said.
About 1,000 residents have been told to leave their homes, and police have warned there could be further evacuations.
The explosion happened shortly before midnight local time (2300 BST) when one wagon of the train, travelling from La Spezia to Pisa, came off the tracks before ploughing into several homes near the station in Viareggio.
"It was a derailment that caused the explosion of one of the rail cars filled with liquefied natural gas. It was a very strong explosion," Viareggio Mayor Luca Lunardini said.
The BBC's Duncan Kennedy, in Viareggio
There is a containment operation going on - firefighters are trying to make sure none of the other gas tanks explode.
Viareggio is almost like a seaside town, full of tourist shops and gift shops. It's never known anything like this.
In the immediate area, many of the buildings were flattened and a rescue operation has been going on to pull people free and find survivors.
The emergency services personnel are working in extremely dangerous conditions, bearing in mind that the train has not yet been declared safe.
"Two buildings collapsed and burned down, there are others in a serious condition," he said.
A senior firefighter, Antonio Gambardella, said the force of the blast had turned cars on to their sides.
"The gas spread out among the nearest houses before exploding," he told AFP.
One witness described the scene as "apocalyptic".
"A young man with a child jumped out of a window to save themselves - a scene I hope never to re-live because I was really afraid," he told Reuters.
"People just couldn't do anything because with fire there is just nothing you can do, but we somehow managed to survive without any injury."
Another witness, Penny Firth, told the BBC: "The explosion was terrifying. The whole sky turned orange and there was a huge mass of dense smoke, we could feel the heat intensify."
Several of the victims, including at least one child, died when their homes collapsed with the force of the blast. At least two other people are thought to have been killed on the road next to the station.
Three children were pulled alive from their burnt homes early on Tuesday.
The Civil Protection Department called in specialist teams with equipment for dealing with nuclear, biological and chemical threats.
Police say the incident may have been caused by damage to the tracks or a problem with the train's braking system.
Railway unions are blaming old and obsolete rolling stock.
The train's two engineers, who were only slightly injured, said they felt an impact about 200m (650ft) outside the station, shortly before the rear of the train derailed, officials say.
One of them said it was "a miracle" that he managed to escape after his cabin filled with the liquid gas.
Liquefied petroleum gas is a mixture of propane and butane that is used for cooking or as fuel for specially-adapted vehicles.
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