At least 75 people have been killed after a magnitude 7.2 earthquake hit eastern Turkey, state-run TRT television reports.
But Turkey's Kandilli Observatory estimated that 500 to 1,000 people could have perished in Van province on Sunday.
The seismology institute's estimate was based on the strength of the quake and the structure of the housing in the area.
The worst damage was caused to the town of Ercis, close to the Iranian border. The city of Van also suffered substantial damage.
"Around 10 buildings have collapsed in the city of Van and around 25 or 30 have collapsed in Ercis, including a dormitory,'' Deputy Prime Minister Besir Atalay said.
Atalay said authorities had no information yet on remote villages, but a local governor was touring the region by helicopter to assess damage.
TRT said 59 people had been killed and 150 others injured in Ercis, while 15 others died in Van. Another person died in the nearby province of Bitlis.
The quake's epicentre was in the village of Tabanli.
Al Jazeera’s Murat Utku, reporting from Van, said rescue workers were are scrambling to rescue those trapped before nightfall.
"The heat difference between day and night is very big here", he said. "Some are trying to dig their family members out by hand, but some machines are being taken here now to join the rescue workers."
The temperature was expected to dip to three degrees Celsius during the night.