Turkey's Prime Minister flew to eastern Turkey Sunday to see for himself the devastation wrought by a 7.2-magnitude earthquake that has killed more than 70 people.

"There are more than 70 dead in Van province," Huseyin Celik, deputy leader of the ruling Justice and Development Party (AKP), told the private NTV television channel.

Some 50 of them were killed in Ercis, a district of around 100,000 people in the same region, where the most serious damage occured, said Celik.

He was accompanying the prime minister, who flew to the quake region after cancelling his official programme.

The quake that struck Van, a large eastern city populated mainly by Kurds, was Turkey's strongest in years. The US Geological Survey initially measured the quake at 7.3 magnitude but later downgraded it to 7.2.

Officials said many buildings had collapsed in Ercis and Van, and fears were running high that the toll could increase as many people were trapped in collapsed buildings.

"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, as officials warned they were struggling to assess the extent of the damage.

Between 500 and 1,000 people were estimated to have been killed in the quake, Mustafa Erdik, director of the Kandilli seismological institute in Istanbul, told reporters in an initial assessment.

At least 50 people were taken to hospital in Van and nearly a thousand people in Ercis.

"Many buildings alongside a major street in Ercis were collapsed," said an AFP photographer at the quake scene, who added that the power was out throughout the district. "People are using lanterns," he said.

Television footage showed panicked residents using shovels and other digging tools trying to rescue people trapped under collapsed buildings in Ercis and Van.

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," Bekir Kaya, the mayor of Van, told NTV television.

US President Barack Obama offered his condolences to the victims of the massive quake and said the United States stood read to assist the country's authorities.

"We stand shoulder to shoulder with our Turkish ally in this difficult time, and are ready to assist the Turkish authorities," he said in a statement.

Some 1,275 search and rescue teams from 38 Turkish cities as well as 145 ambulances were sent to the quake region, according to media reports.

The military said six batallions were also involved in search and rescue efforts, in a statement posted online.

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

Some 200 inmates fled the prison in Van province, which was damage in the quake, media reports said. But 50 of the inmates returned to prison later, they added.

The epicentre of the quake, which struck around 1041 GMT, was at Tabanli in Van province, Turkey's Kandilli institute said. Two aftershocks had hit the villages of Ilikaynak and Gedikbulak in particular, it added.

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. It did not report any deaths or serious damage.

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