Desperate survivors of a powerful earthquake in eastern Turkey dug into the rubble with their bare hands Sunday, trying to reach those trapped and injured. The quake collapsed dozens of buildings and killed at least 138 people, Prime Minister Recep Tayyip Erdogan said, though the death toll was expected to rise.

Erdogan said 93 people died in the city of Van and 45 in the nearby town of Ercis, but at the very least, that tally seemed to exclude a child reported dead in the neighbouring province of Bitlis, while hundreds more people remained unaccounted for.

State-run TRT television reported inmates escaped from a prison in the region soon after the quake hit.

People were still trapped under rubble overnight, Erdogan said. More than 350 survivors sustained injuries.

Several aftershocks were reported late Sunday, including a 6.0 magnitude temblor that struck six kilometres southeast of Van.

Officials in the mountainous eastern region, one of the country's poorest, were among those fearing the earthquake's toll will be much higher.

The Reuters news agency quoted a local crisis centre saying that nearly 600 have been injured and another 400 have been reported missing.

About 45 buildings, including a student dormitory, collapsed in the most powerful quake to hit this part of Turkey in at least a decade, Deputy Prime Minister Besir Atalay said.

The earthquake struck eastern Van province, close to the Iranian border, at 1:41 p.m. local time, Turkey's National Earthquake Monitoring Centre said. The centre reported the quake's magnitude as 6.6, while the United States Geological Survey said it measured 7.2.

Atalay said 25 to 30 buildings collapsed in Ercis, near the Iranian border on Lake Van, and about 10 in the city of Van to the south. Video from Ercis, home to about 80,000 people, showed panic-stricken residents running through the streets in clouds of dust.

Next to a flattened eight-storey building, which had shops on the ground floor, residents sobbed, hoping their missing relatives would be rescued.

"My wife and child are inside! My four-month-old baby is inside!" CNN-Turk television showed one young man crying.

Late Sunday, Israeli Defence Minister Ehud Barak said the Turkish government turned down Israel's offer of aid. Once close allies, relations between Israel and Turkey were damaged by a 2010 Israeli raid on a Gaza-bound flotilla in which nine Turks were killed.

Barak said the offer of aid remains open.

Turkish officials said they've declined similar offers from a dozen other countries as well.

The quake had a depth of 20 kilometres, according to the U.S. geological survey, which is relatively shallow and could potentially cause more damage. It touched off a day of intense seismic activity in the area, with at least 29 subsequent tremors registering a magnitude 4.0 or higher.

Telephone and other services were knocked out, and search and rescue teams from other parts of Turkey were being forced to land at an airport a 90-minute drive away on damaged roads.

"There are so many dead," Zulfikar Arapoglu, the mayor of Ercis, told NTV television. "Several buildings have collapsed, there is too much destruction. We need urgent aid, we need medics."

Earthquakes are frequent in Turkey, which is crossed by fault lines. In 1999, about 18,000 people were killed by two powerful earthquakes that struck northwestern Turkey. Authorities blamed shoddy construction for many of the deaths.

Many buildings in Van province, with a population of about 350,000, are also old and poorly built, unlike those in Istanbul and other more affluent areas, where the government has insisted on better engineering and buildings able to withstand quakes.

According to the Ercis municipal website, town meetings earlier this year focused on earthquake safety in the town, located in one of Turkey's most quake-prone zones. Officials promised to crack down on shoddy, unlicensed construction.

"We may only need earthquake-safe buildings for only 30 to 40 seconds every 30 to 40 years, but we need those buildings right now," Arapoglu is quoted as saying. "You can't guess when there will be an earthquake."