Istanbul, Turkey (CNN) -- As night fell over eastern Turkey on Sunday following the most powerful earthquake in at least a decade, citizens were using flashlights and shovels as they clambered over the rubble of collapsed buildings looking for survivors.
At least seven aftershocks rattled the region, one of the nation's poorest. The extent of casualties was not immediately known.
Some 25 apartment buildings and a student dormitory collapsed in the town of Ercis on the north shore of Lake Van, the Turkish Red Crescent said.
Local rescuers took many wounded people out of the dormitory, the Red Crescent statement said, without saying exactly how many.
A health services building also collapsed, along with part of a hospital, CNN sister network CNN Turk reported. At least two doctors were thought to be in the rubble of the health services building, the network said. The injured were being treated in the hospital's garden.
Official rescue efforts were under way in Ercis, said CNN Turk reporter Sevda Incesu, but residents were also conducting efforts of their own. Ambulances were having trouble getting into town because the roads were littered with rubble, she said.
Video footage from the scene showed one man freed from the rubble being loaded onto a stretcher in a neck brace and put into an ambulance amid a crush of rescue workers and bystanders.
The Red Crescent called for rescue workers, heavy machinery and drinking water, and set up a crisis desk in the capital Ankara.
Deputy Prime Minister Besir Atalay said 10 buildings had collapsed in the center of the city of Van, citing local authorities.
Health Minister Recep Akdag said an air ambulance and several helicopters would go to the quake zone.
Television pictures from Van province showed rescuers and members of the public climbing over massive piles of cinder blocks that had been a building before the earthquake hit.
Ambulances and bulldozers were on the scene.
A seven-story building collapsed on Kazim Karabekir Street in the city of Van, and more buildings were reduced to rubble the village of Tabanli in Van province, the Anatolian news agency said. It was unknown how many people were trapped.
Video from CNN Turk showed the inside of shaking buildings, and people gathering outside on the streets.
Prime Minister Recep Tayyip Erdogan was expected to arrive in the area later Sunday, his office said.
Israel offered Turkey "any help it may require" after the earthquake, Defense Minister Ehud Barak's office said. Israel and Turkey, once close allies, saw a deterioration in relations in a dispute over an Israeli naval commando raid on the Gaza-bound ship Mavi Marmara, in which nine Turkish activists were killed.
Turkey is "no stranger to having these seismic events," but Sunday's quake is considered major, CNN Meteorologist Reynolds Wolf reported.
The U.S. Geological Survey initially reported the quake had a magnitude of 7.3, then revised it down to 7.2.
The last quake of that magnitude in Turkey -- a 7.2 tremor in Duzce in 1999 -- killed 894 people, the USGS reported. A 7.6 earthquake in Izmit, Turkey, killed more than 17,000 people the same year, according to the USGS.
Sunday's major quake hit at 1:41 p.m. local time and was followed by at least seven aftershocks, American and Turkish monitoring agencies reported.
It took place about 12 miles from Van, the USGS said.
An official Turkish monitoring office reported aftershocks ranging in magnitude from 2.6 to 5.8, all within an hour of the first quake.
The USGS reported a depth of 4.5 miles, or 7.2 kilometers; the center in Turkey said the quake was about 3 miles, or 5 kilometers, deep.
One concern is displacement of water along Lake Van, which could send water gushing into nearby areas, particularly along the west side, Wolf reported.
The European Commission and the British government were among those offering condolences, and the British offered assistance.
"We are greatly saddened by the news of the terrible earthquake that has struck the Van province in southeast Turkey," European Council President Herman Van Rompuy said European Commission President Jose Manuel Barroso said in a joint statement. "Our thoughts are with the injured and the families of the victims and we should like to convey our condolences to the people and authorities of Turkey."
British Foreign Secretary William Hague said in a statement, "Today's earthquake in eastern Turkey has caused immense destruction, resulting in terrible loss of life. I send my deepest condolences to the friends and loved ones of those who have died or been affected. My thoughts are with those who are anxiously awaiting news from the rescue efforts. The UK is ready to provide assistance in line with any request from Turkish authorities. We stand with Turkey at this difficult time."
In Libya, where leaders of the interim National Transitional Council declared the country liberated Sunday following the death of former leader Moammar Gadhafi, NTC chairman Mustafa Jalil also offered condolences.