A packed express train travelling from Istanbul to the Turkish capital Ankara derailed this evening, killing 139 people, in one of Turkey's worst rail disasters in history, officials said.
"A total of 139 people were killed, and another 57 people were injured," a Health Ministry official told reporters.
Officals suspect the accident was caused by a mechanical fault. Transport officials said one of the rear wagons may have derailed first, pulling others off the line, CNN Turk television said.
"Four wagons were derailed and fell on their sides," Mr Mehmet Ayci of the state railways agency told Reuters. "We don't believe speed was the cause, because the train was travelling slower, between 75-80 km per hour (45-50 mph), in this area."
The head of a crisis centre, Mr Muammer Turker, told reporters the train was carrying 234 passengers and nine crew.
The train came off the rails near the town of Pamukova at around 7:45 p.m. (local time), almost two hours after leaving Istanbul, Turkey's commercial hub and biggest city.
Many of the victims were children, CNN Turk said and showed pictures of rescue workers carrying crying children covered in blood into a hospital.
"There are pieces of bodies everywhere, limbs have been severed," Mr Oguz Dizer, a journalist at the scene, told CNN Turk.
The new fast train connecting Ankara with Istanbul went into service in June amid much fanfare. Critics have said Turkey's decrepit train system was in need of complete modernisation and was not capable of running high speed services.
"Using the old track and simply making changes to accelerate the train was a grave mistake. Railway experts who said it was not possible to use this track were ignored," former transport minister Mr Oktay Vural told CNN Turk.
Passenger Ocrun Acabey told NTV he was in a wagon where victims suffered slight injuries.
"Before the crash, the train shook strongly two or three times at bends. First we swung to the left, then the carriage turned over to the right," he said, adding the train had not shaken like that on the many previous trips he had taken.
Prime Minister Mr Tayyip Erdogan, who helped launched the train at a gala ceremony, was heading to the scene of the disaster.
"This is a huge disaster, and our sadness is great ... I express my condolences to the families of the victims," he said.