Firemen have been pumping out and burning off the gas in the wagons
Two children badly burned when a train exploded as it passed through an Italian town have died of their injuries, taking the death toll to 16.
The three-year-old girl and the two-year-old boy had both suffered burns on 90% of their bodies, officials said.
At least a dozen other people remain in a critical state, according to reports.
The accident happened in the northern town of Viareggio on Monday night, when a train carrying gas tanks jumped the tracks and exploded near houses.
Investigators want to know whether a broken axle may have been responsible.
The blast caused two buildings - described as houses or small blocks of flats - to collapse while others were set on fire.
The accident happened shortly before midnight, when most people would have been at home.
Elia Quiroz, who lives near the town's railway station, said he was about to go to bed on Monday night when his kitchen table started shaking.
"Then I heard an explosion and I went outside. I saw flames as high as 30, 40 metres, and I ran," he told the Associated Press.
Fire crews have been working to clear the scene, while residents are still being kept away from their homes amid fears other gas tanks might be at risk of exploding.
By Wednesday morning six of the 13 remaining wagons of the freight train had been made safe, fires services said.
Prime Minister Silvio Berlusconi travelled to the town on Tuesday to witness the emergency operation, but was greeted by a jeering crowd.
The region is left-leaning and it was unclear whether the boos were politically motivated, had any relation to recent scandals involving the prime minister, or were a reaction to the accident, correspondents say.
Local people have demanded to know why gas was being transported so close to people's houses.
The cause of the accident is unclear, though one of the main theories being investigated is that an axle on one of the gas wagons broke, causing it to derail.
Railway unions blamed old and obsolete rolling stock.
But the company that owned the wagon, a subsidiary of US-based GATX Corp, said the unit was new, and that so far there was no evidence of "any connection between the cause of the accident and our wagons".
Earlier police said the incident may have been caused by damage to the tracks or a problem with the train's braking system.