A powerful earthquake with a magnitude of 6.6 shook southeastern Turkey on Sunday, Turkey's Kandilli Observatory said, triggering the collapse of buildings and killing many people, according to a local mayor.

State-run media reported 50 people had been injured, while the prime minister's office said the earthquake had caused a loss of life and damage. No figures were available on the death toll.

A lot of buildings collapsed, many people killed, but we don't know the number. We are waiting for emergency help, it's very urgent, Zulfukar Arapoglu, mayor of the badly hit Ercis district, told news broadcaster NTV.

We need tents urgently and rescue teams. We don't have any ambulances, and we only have one hospital. We have many killed and injured, he said.

Emergency teams were trying to rescue people believed to be trapped in a building in Van, near the Iranian border, state-run news agency Anatolian said. It said 50 injured people had been taken to hospital in Van, but did not give details on how serious their injuries were.

The Kandilli Observatory said the earthquake struck at 1041 GMT and was 5 kilometers (3.1 miles) deep. The U.S. Geological Survey earlier reported the magnitude was 7.6.

Television pictures showed damaged buildings and vehicles, crushed under falling masonry, and panicked residents wandering in the streets.

Turkish media said phone lines and electricity had been cut off. Prime Minister Recep Tayyip Erdogan was heading to Van to see the damage, media reported.

Aftershocks continued after the initial quake, whose epicenter was at the village of Tabanli, north of Van city, media reported.

In Hakkari, a town around 100 kilometers (62 miles) south of the city of Van in southeastern Turkey, a building could be felt swaying for around 10 seconds during the quake.

There was no immediate sign of any casualties or damage in Hakkari, around two-and-one-half hours drive through the mountains from Van, around 20 kilometers (12.2 miles) from the epicenter.

Major geological fault lines cross Turkey and small earthquakes are a near-daily occurrence. Two large quakes in 1999 killed more than 20,000 people in northwestern Turkey.

Two people were killed and 79 injured in May when an earthquake shook Simav in northwestern Turkey.

(Additional reporting by Seda Sezer and Daren Butler; Editing by Alison Williams)