Rescue workers were continuing to search for some 30 people buried under the rubble of collapsed buildings in Elazig province and neighboring Malatya, said Health Minister Fahrettin Koca. He warned that the death toll could rise.
Emergency workers and security forces distributed tents, beds and blankets as overnight temperatures dropped below freezing in the affected areas. Mosques, schools, sports halls and student dormitories were opened for hundreds who left their homes after the quake.
"The earthquake was very severe, we desperately ran out (of our home)," Emre Gocer told the state-run Anadolu news agency as he sheltered with his family at a sports hall in the town of Sivrice in Elazig. "We don't have a safe place to stay right now."
The quake hit Friday at 8:55 p.m. local time (1755 GMT) at a depth of 6.7 kilometers (around 4 miles) near Sivrice, the Disaster and Emergency Management Presidency, or AFAD, said. Various earthquake monitoring centers gave magnitudes ranging from 6.5 to 6.8.
AFAD said it was followed by 228 aftershocks, the strongest with magnitudes 5.4 and 5.1.
At least five buildings in Sivrice and 25 in Malatya province were destroyed, said Environment and Urbanization Minister Murat Kurum. Hundreds of other structures were damaged and made unsafe.
AFAD said in a statement that 17 people were killed in Elazig and four in Malatya. Some 1,030 people were hurt.
Television footage showed emergency workers removing two people from the wreckage of a collapsed building in the town of Gezin. Another person was saved in the city of Elazig, the provincial capital, and two more from a house in Doganyol, Malatya.
AFAD said 28 rescue teams were working around the clock. More than 1,300 personnel from 39 of Turkey's 81 provinces were sent to the disaster site.
"Our biggest hope is that the death toll does not rise," Parliament Speaker Mustafa Sentop said.
Communication companies announced free telephone and internet services for residents in the quake-hit region, while Turkish Airlines announced extra flights.
Interior Minister Suleyman Soylu said emergency work was proceeding under the threat of aftershocks.
Turkish President Recep Tayyip Erdogan said on Twitter overnight that all measures were being taken to "ensure that the earthquake that occurred in Elazig and was felt in many provinces is overcome with the least amount of loss."
Neighboring Greece, which is at odds with Turkey over maritime boundaries and gas exploitation rights, offered to send rescue crews should they be needed.
Elazig is some 565 kilometers (350 miles) east of the Turkish capital, Ankara.
Turkey sits on top of two major fault lines and earthquakes are frequent. Two strong earthquakes struck northwest Turkey in 1999, killing around 18,000 people.
A magnitude 6 earthquake killed 51 people in Elazig in 2010.