At least 23 people died and dozens were injured when two passenger trains collided head-on in southern Italy on Tuesday, according to fire service officials.
The crash on Tuesday happened on a single stretch of track in countryside between the towns of Corato and Andria.
An aerial image showed carriages smashed and crumpled by the force of the impact, with debris flung out among olive trees which flanked both sides of the track. Both rails were made up of four carriages.
"We are working with dozens of rescue teams to open up the carriages," said Luca Cari, a fire service spokesman, adding that they had saved a young boy from the wreckage.
"The rescue is complicated because this happened in the middle of the countryside," he said.
There was no immediate reason given for the collision, which took place at around 11:30am (09:30 GMT) in the region of Puglia.
'Human error likely'
However, investigators were quoted by the AFP news agency as saying it was likely that the collision was caused by human error.
One of the four-carriage trains was supposed to have waited at a station for a green light before heading down the single track between Corato and Andria, investigators reportedly said.
Prime Minister Matteo Renzi said that authorities "will not stop until a clear explanation over what happened is provided.
"This is a moment for tears in which we need to work to recover the victims and wounded," he added, cutting short a visit to Milan in northern Italy to return to Rome.
The stretch of track is operated by the regional rail company Ferrotramviaria. It was not clear how many people had been on the trains.
The last major rail disaster in Italy was in 2009 when a freight train derailed in Viareggio, in the centre of the country, with more than 30 people living close to the tracks killed in the subsequent fire.