The huge quake toppled buildings, triggering a frantic search for survivors.
The epicentre was near the Turkish city of Gaziantep, a major Turkish provincial capital of more than two million people.
A second earthquake of 7.5 magnitude hit central Turkey on Monday afternoon, according to the European-Mediterranean Seismological Centre and US Geological Survey.
Turkey And Syria Earthquake | February 2023
Turkish president Recep Tayyip Erdogan said 912 have died in the country, with at least 5,383 people injured across 10 provinces affected by the quake and 1,700 buildings collapsed. He said 45 countries, including the UK, had offered support.
The Syrian health ministry said 326 people had been killed and some 1,042 injured there, most in the provinces of Hama, Aleppo and Latakia, where numerous buildings collapsed. The death toll was expected to rise further.
British Prime Minister Rishi Sunak offered his condolences to Turkey and pledged support from the UK.
He tweeted: “My thoughts are with the people of Türkiye and Syria this morning, particularly with those first responders working so valiantly to save those trapped by the earthquake. The UK stands ready to help in whatever way we can.
“Millions of people across Turkey, Syria, Lebanon, Cyprus and Israel felt the earthquake.”
The first earthquake struck at 4.17 am local time at a depth of about 11 miles, the US Geological Survey said. Videos and pictures from across the region showed the destruction wrought.
One clip from the border town of Azaz, Syria, showed a rescuer desperately running through a field of debris with an injured child in his arms, while another showed the total collapse of a seven-storey building in Sanliurfa, Turkey.
He tweeted: “Saddened about the loss of lives in Turkey and Syria following the major earthquake. Our thoughts go to the victims and their loved ones. I have sent my deepest condolences to Tayyip Erdogan. As partner of Turkey and holder of the EU presidency, we stand ready to offer our support.”
British foreign secretary James Cleverly also said the UK stands ready to help, tweeting: “Tragic loss of life in the Turkey and Syria earthquake. Our condolences go to the families of those who died and our thoughts are with the survivors. The UK stands ready to provide assistance.”
The earthquake came as the Middle East is experiencing a snowstorm that is expected to continue until Thursday.
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.