An earthquake of 7.3 magnitude rocked eastern Turkey on Sunday, with a seismological institute saying up to 1,000 people could lie dead under the rubble of dozens of collapsed buildings.

Turkey's strongest earthquake in years struck Van, a large eastern city populated mainly by Kurds.

"Five hundred to 1,000 people are estimated to have been killed in the quake," Mustafa Erdik, director of the Kandilli seismological institute in Istanbul, told reporters.

Earlier reports had not mentioned casualties, but many were feared trapped in collapsed buildings and officials warned they were struggling to assess the extent of the damage.

"There is serious human and material loss," said a brief statement from the national disaster body, which is based in the prime minister's office.

Officials said around 50 buildings had collapsed, including a dormitory.

At least 50 people were taken to hospital in Van and nearly a thousand people in Ercis, a district of around 100,000 people in the same region, where the most serious damage occured, according to media reports.

"Many buildings alongside a major street in Ercis were collapsed," said an AFP photographer at the quake scene.

"There is electricity cut throughout district. People are using lanterns," he said.

Television footage showed panicked residents using shovels and other digging tools trying to rescue people trapped under a collapsed eight-storey building in the city centre.

Seach and rescue teams were using electrical generator lights to help the search for trapped victims as the night fell.

"An eight-storey apartment collapsed," a local from Ercis told AFP.

"There are efforts to rescue people but the loss is big. I myself saw three to four dead," he added.

Most people are expected to spend the night outdoors, with the temperature expected to dip to three degrees Celsius (37 Fahrenheit).

"People are panicked. The telecommunication services have collapsed. We cannot reach anybody," Van Mayor Bekir Kaya told NTV television.

The government was due to send satellite phones to the region, according to media reports.

Six helicopters, including four ambulance helicopters, as well as C-130 military cargo planes were sent to the area carrying tents, food and medicine.

The US Geological Survey measured the quake at 7.3 magnitude and said an aftershock of 5.6 magnitude had also been registered. It placed the epicentre of the aftershock, which happened at 1056 GMT, at 19 kilometers (12 miles) northeast of Van.

The depth of the initial quake was 7.2 kilometers (4.5 miles), according to the US seismologists. The depth of the aftershock was 20 kilometers, they added.

The epicentre of the quake, which struck around 1041 GMT, was at Tabanli in Van province, the Kandilli institute said.

The Turkish institute said there were two aftershocks which affected the villages of Ilikaynak and Gedikbulak in particular.

Prime Minister Recep Tayyip Erdogan cancelled his official programme and was due to visit the quake region on Sunday, NTV said.

Although the quake damaged Van's airport it did not disrupt the air traffic, the Anatolia news agency reported, citing civilian aviation authorities.

Van, a city of 380,000 mainly Kurdish inhabitants, is more than 1,200 kilometres from the capital Ankara.

The quake was also felt across the border in northwestern Iran, causing some panic in major cities, Iranian media reported, but without any mention of casualties or damage.

The tremors were strong enough to cause "scenes of panic among the population of the cities," according to several Iranian media.

Earthquake-prone Turkey lies atop several fault lines.

In 1999, two strong quakes in the heavily populated and industrialised regions of northwest Turkey left some 20,000 dead.

And a powerful earthquake in the town of Caldiran in Van province killed 3,840 people in 1976.