According to Deputy Prime Minister Besir Atalay, 239 people died and 1,300 were injured in the massive earthquake.
The city of Ercis was the worst-hit, where more than 80 buildings fell.
Tens of thousands of people have been sleeping outside in freezing conditions last night.
Turkey is particularly vulnerable to earthquakes because it sits on major geological fault lines.
Two earthquakes in 1999 with a magnitude of more than 7 killed 18,000 people in densely populated parts of the north-west of the country.
The earthquake was followed by a series of powerful aftershocks, also centered north of Van, including two of magnitude 5.6 soon after the quake and one of 6.0 late on Sunday.
Turkish Prime Minister Recep Tayyip Erdogan has been visiting the affected area by helicopter.
The prime minister said that villages close to Van were the worst affected as most buildings there were made of clay bricks.
He thanked other countries for their offers of help, but said Turkey could cope with the disaster on its own.
Up to 80 buildings, including a dormitory, collapsed in the worst-hit city of Ercis, about 60km north of Van, while 10 fell in Van itself.
Ambulances, soldiers and rescue teams rushed to Ercis, a Reuters photographer reported.
Survivors complained of a lack of heavy machinery to remove chunks of cement floors that had pancaked on to each other, the Associated Press reports.
There were also reported serious damage and casualties in the district of Celebibag, near Ercis.
“There are many people under the rubble,” said Celebibag mayor, Veysel Keser.
“We can hear their screams for help. We need urgent help.”
According to Turkey’s seismology institute, Kandilli Observatory, hundreds of people could have been killed.
Turkish seismologist Polat Gulkan claimed that building regulations were often ignored in Turkey.
“The enforcement of the code provisions is not at the standard that we would like to see it,” Polat Gulkan said.
It was reported that residents of Van and Ercis have been spending the night huddled around camp fires in the open air, fearing more aftershocks.
Rescuers could be seen working by torchlight, using their bare hands and shovels.
The earthquake cut electricity and telephone lines and the authorities in some areas have cut gas to avoid the risk of fire.
More search and rescue teams were being sent from other parts of the country.
Hakki Erskoy, from the Turkish Red Crescent, said aid teams from the north and east of Turkey were being sent to the earthquake-hit area.
Hakki Erskoy said camps were being set up to shelter people and blankets, and that food and water were being sent, along with mobile kitchens.
Military aircraft were being deployed to help with the rescue and relief efforts, Hakki Erskoy said.
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