"According to our first estimates, 10 people lost their lives and 73 people were injured", Eyup Gumus, the Turkish Health Ministry's undersecretary, was quoted as saying.
Turkey's official Anadolu news agency said two engineers were called in for questioning at the prosecutor's office.
The Ministry of Transport, Maritime Affairs and Communications said in a statement the accident happened after the railway track slipped down from its original spot due to heavy downpour.
The Turkish army said in a statement that it sent helicopters to the scene, while the Istanbul municipality on Twitter said 24 rescue workers and six rescue vehicles were on their way to provide assistance.
Television footage showed numerous injured being carried away on stretchers as the train carriages lay on their sides.
Television footage shows rescuers heading to the crash site, and victims pulled from the carriages.
Dying declarations of Nirbhaya true, voluntary, consistent: SC
Elizabeth Hospital in Singapore in the early hours at 4.45 am local time (2.15 am IST) after battling severe injuries for 13 days. The fourth did not appeal, but his lawyer said they would soon file one, according to the Press Trust of India news agency.
Russian news reports said that Russian tourists were on the train when it derailed.
Turkey's audiovisual authority RTUK later said the government had issued a temporary ban on broadcasting images from the scene.
President Recep Tayyip Erdogan's office said he had received information from the ministers of transport and interior about the incident, and sent condolences for those killed.
Over the past few years, Turkish cities have been building high-speed rail lines to replace the country's ageing network.
The train, carrying 362 passengers and six train staff, was traveling from Edirne province to Istanbul when five bogies derailed near Sarilar village of Tekirdag's Corlu district on Sunday.