At least 10 deaths were reported initially in Turkey.
In northwest Syria, the opposition’s Syrian Civil Defense described the situation in the rebel-held region as “disastrous” adding that entire buildings have collapsed and people are trapped under the rubble.
The civil defense urged people to evacuate buildings to gather in open areas.
The U.S. Geological Survey said quake was centered about 33 kilometres (20 miles) from Gaziantep, a major city and provincial capital.
It was about 26 kilometres from the town of Nurdagi.
It was centered 18 kilometres deep, according to the US Geological Survey.
A strong 6.7 temblor rumbled about 10 minutes later.
Turkey’s Disaster and Emergency Management agency, AFAD, said the quake measured 7.4 and was centered in the town of Pazarcik, in Kahramanmaras province.
In Sanliurfa, at least 10 deaths have been confirmed, according to Gov. Salih Ayhan.
Several buildings tumbled down in the neighboring provinces of Malatya, Diyarbakir and Malatya, HaberTurk television reported. There was no immediate reports on casualties.
Turkey sits on top of major fault lines and is frequently shaken by earthquakes.
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The earthquake was also felt in Lebanon and Syria.
Syria’s state media reported that some buildings collapsed in the northern city of Aleppo and the central city of Hama.
In Syria’s rebel-held northwest that borders Turkey several buildings collapsed, according to the opposition’s Syrian civil Defense.
In Damascus, buildings shook and many people went down to the streets in fear.
The quake jolted residents in Lebanon from beds, shaking buildings for about 40 seconds.
Many residents of Beirut left their homes and took to the streets or drove in their cars away from buildings.
There were no immediate reports of major damage or casualties in either country.
Turkey sits on top of major fault lines and is frequently shaken by earthquakes.
Some 18,000 were killed in powerful earthquakes that hit northwest Turkey in 1999.
This is a developing story. More to come.