Ten people were killed and 73 injured on Sunday when a train packed with weekend passengers derailed in northwest Turkey, the health ministry said.
The train, with over 360 people on board, was travelling from the Edirne region on the Greek and Bulgarian borders to Istanbul's Halkali station when six of its carriages derailed in the Tekirdag region.
Over 100 ambulances have been sent to the scene, state-run TRT Haber television said TRT Haber said, quoting Health Ministry Undersecretary Eyup Gumus.
The Turkish army said in a statement that it had sent helicopters to the scene.
Television pictures showed several train carriages laying on their sides, and shocked injured being taken away on stretchers as rescue workers picked through the wreckage.
"There are a large number of injured and we have fatalities," Tekirdag governor Mehmet Ceylan told the NTV channel. "The accident happened because of adverse weather conditions," he added.
Reports said the surrounding area was muddy due to recent rains and the ground beneath the rails may have subsided away, causing the train to derail.
The train derailed outside the village of Sarilar in the Corlu district of Tekirdag, reports said.
President Recep Tayyip Erdogan has been informed over the accident and expressed his condolences over those who lost their lives, state-run Anadolu news agency said.
Turkish authorities under Erdogan have over the last years sought to modernise Turkey's once ramshackle rail network, building several high-speed inter-city lines.
Turkish passengers have in general preferred taking planes or the bus for inter-city travel but this is changing with the new high-speed lines.
The train involved in the accident appeared to be one of the slower passenger trains travelling on a single track railway.
Turkey's rail network has been hit by several fatal accidents over the last years.
In January 2008, nine people were killed when a train derailed in the Kutahya region south of Istanbul due to faulty rails.
And in Turkey's worst recent rail disaster, 41 people were killed and 80 injured in July 2004 when a high-speed train derailed in the northwestern province of Sakarya.