Fire officials said the gas tankers derailed and exploded shortly after midnight, and the flames spread rapidly to engulf a nearby road and 10 houses.
Witnesses said the explosion was "like a bomb". At least 35 people suffered serious burns.
Some houses in the area were evacuated and five buildings reportedly collapsed with the force of the explosion.
Firefighters combing the vicinity found one child still alive in the rubble. As many as 300 firefighters were involved in the rescue efforts.
Their search was being made more difficult by the threat that other derailed gas tankers could explode.
Officials were still to determine the cause of the accident.
The Italian state railway company said no trains had collided but said material fatigue in the exploded tanker was a possible cause.
The explosion occurred after a 14-car train coming from La Spezia on its way to Pisa passed through the station.
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