The train, with 360 people on board, was travelling from Kapikule on the Bulgarian border to Istanbul when six of its carriages derailed in the Tekirdag region.
Reports said the surrounding area was muddy due to recent rains.
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.
The train involved in the accident appeared to be one of the slower passenger trains travelling on a single track railway.
Publication ban issued over the news about accident.
