Local media said at least two carriages derailed.
The train was en route from Ankara to the central Turkish city of Konya on Thursday morning.
The train ploughed into a railway engine and then a pedestrian overpass at Marsandiz station, said officials. Rescue teams were working at the scene.
"Our hope is that there are no other victims", said Sahin.
Video footage from the scene shows rescue workers trying to free people who were trapped in beneath the mangled metal wreckage of the overpass at the Marsandiz train station.
It was also not yet known if anyone was walking on the overpass when it was struck by the train.
The head-on collision between the high-speed train and the pilot engine, which was returning from checking the rails, occurred around six minutes after the first' departure from Ankara terminal at 06.30 (0330GMT), Turhan added.More news: Raptors' Kawhi Leonard shoots down Christmas question
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Three of those were severely injured, according to the governor's office.
Governor Vasip Sahin told reporters that 4 people were killed and 43 others were taken to area hospitals.
The accident comes after another train disaster in July, when 24 people were killed and hundreds more injured after a train derailed in Tekirdag province, north-west Turkey, due to ground erosion following heavy rains.
In the summer, several people were killed and dozens injured after a train crashed in Tekirdağ province - on the European side of Istanbul.
The public prosecutor in Ankara has launched an investigation into the crash, according to state news agency Anadolu.
The Ankara to Konya high-speed route was launched in 2011 and was followed in 2014 with a high-speed link between Ankara and Istanbul.
Konya, about 160 miles south of Ankara, is home to the tomb of the Sufi mystic and poet Jalaladdin Rumi, attracting thousands of pilgrims and tourists.