AFP - Two gas-filled rail tankers exploded after derailing in northern Italy, engulfing homes in flames, killing at least 15 people and injuring dozens more, firefighters said Tuesday.
  
The blast in the seaside resort of Viareggio also seriously injured 34 people, about half of whom were in a critical condition.
  
Many victims had suffered extensive burns, said the firefighters' coordination centre in Rome.
  
Two casualties died Tuesday, raising the initial toll of 13.
  
Hundreds of firefighters from across the region were rushed to the area to help with the rescue operation and ensure the remaining tankers did not catch fire.
  
A thousand people have been evacuated from the area because of the danger of more explosions, said Luca Lunardini, mayor of the city of 50,000 people.
  
The region has declared a state of emergency and Transport Minister Altero Matteoli is to set up a committee to investigate the incident.
  
The explosion happened just before midnight Tuesday when a wagon in a 14-carriage train transporting liquefied petroleum gas (LPG) came off the rails in the coastal town, which is just northwest of Pisa.
  
Witnesses, including Lunardini, reported hearing three explosions: a violent initial blast and two others just afterwards.
  
"The cars flipped over on their sides on the rails and the gas spread out among the nearest houses before exploding," said senior firefighter Antonio Gambardella.
  
Dozens of small homes along the railway line were caught in the blast. Two small residential buildings were completely engulfed in the flames and destroyed, witnesses said.
  
Around 18 people were believed to live in one of the buildings.
  
Some were known to have survived, Gambardella told AFP, "but we fear there could be several more people under the rubble." Four people have been reported missing.
  

He said an eight-year-old boy had been pulled out alive in the early hours of Tuesday.
  
Another two children were among the wounded, said Aronica, the local prefect.
  
The dead and injured were either passers-by or people who lived in the two buildings destroyed in the blast, but most of them still had to be identified.
  
At least four other buildings were damaged in the explosion.
  
"I heard the explosion and I went out into the street to find myself faced with flames and a motionless charred body lying on the ground," a witness told the Italian news agency ANSA.
  
"It was a terrifying scene which I will never forget," added the witness, who works at a nearby pharmaceutical company. "We couldn't do anything for the body except cover it up."
  
Another witness told how one young girl caught in the blast as she rode past on her scooter had had to throw herself to the ground to put out her burning clothes, ANSA reported.
  
And one of the train drivers told of their escape. "The drivers cabin was filled with the gas, we managed to escape. We are alive, it is a miracle."
  
Investigators were looking into the possibility that the blast happened because the axle on one of the wagons broke, derailing the container and its volatile cargo, said ANSA.
  
Two other wagons were still lying on their side at the crash site Tuesday, with another two still upright, but off the rails.
  
"One of the tasks of the firefighters and notably the specialised chemical accident units is to try to make sure the rest of the tankers don't catch fire and explode," he added.
  
More than 300 firefighters from neighbouring regions were at the scene, he added.
  
Giuseppe Romano, the fire chief for the city of Florence, stressed that work of this kind was very difficult because LPG is very fluid.
  
The train, which started from the port of La Spezia, was going to Pisa.
  
Monday's accident was the most serious in Italy since a cargo train and a passenger service collided on January 7, 2005, killing 17 people and injuring another 60 near the central city of Bologna.
  
Liquefied petroleum gas is a mixture of propane and butane that is used for cooking or as fuel for specially adapted cars.