More than 2,000 people are feared dead after a series of earthquakes struck Afghanistan's remote northern province of Baghlan.
The Afghan Interior Minister, Yunus Qanuni - who has travelled to the area - said up to 20,000 had been left homeless.
Mr Qanuni visited the town of Nahrin, which has been virtually destroyed.
Afghan officials estimated that about 4,000 people had been injured.
The quakes began on Monday and were still producing aftershocks late on Tuesday, hampering rescue efforts.
Afghanistan's interim government pleaded for international assistance as its head, Hamid Karzai, called off a scheduled visit to Turkey.
International aid agencies and the UN have responded to the call.
"It is beyond the interim government to deal with this tragedy," said Mr Qanuni.
"We ask all international agencies and foreign countries to help us in this emergency situation."
The quakes began in the Hindu Kush mountains on Monday at about 1930 local time (1500 GMT), rocking the Nahrin and Burqa districts of Baghlan.
The initial quake measured about six on the Richter scale, and could be felt as far away as Peshawar and Islamabad in Pakistan.
Mr Qanuni said that the bodies of at least 1,800 people had been pulled from the rubble so far.
Ros O'Sullivan, of the aid agency Concern, said that before the quake the area was already considered "high-risk regarding vulnerability to malnutrition," with about 80% of the population receiving relief supplies.
A UN representative in Geneva warned that the quake damage was not necessarily confined to Nahrin and Burqa.
"It would seem that this earthquake is more extensive than thought, is not at all concentrated on these two areas," said Elizabeth Byrs, spokeswoman for the UN Office for Coordination of Humanitarian Affairs.
Fear amongst the rubble
One Afghan commander who flew over the area on Tuesday described the scenes of devastation he witnessed.
"From the helicopter we didn't see any standing homes in and around the villages around Nahrin," General Khalil told the Associated Press news agency.
"Everyone is trying to find the members of their families to bring them out of the destroyed walls or collapsed areas. The earthquake is going on, and each time, the people are very afraid."
A radio operator for the French charity ACTED, which is rushing aid to the scene, said the group's offices in Nahrin had been destroyed.
"There are no non-governmental organisations, there is no hospital, there is no doctor to help these people," said Shoja Zare after speaking to colleagues in Nahrin.
A major relief effort is already under way:
A six-strong international team from the French-based aid organisation Medecins Sans Frontieres is treating the injured in three large tents at the scene and has delivered three lorryloads of aid with a fourth due to arrive
ACTED has dispatched 500 tents and 1,000 blankets to combat the freezing night temperatures
The UN, Red Cross and other aid agencies have sent more than 50 lorries carrying tents, blankets and other supplies from the city of Mazar-e-Sharif, 4.5 hours away
A team of UN and aid experts has left for Afghanistan to assess the needs of the survivors
The British-led International Security Assistance Force (ISAF) in Afghanistan has sent a Chinook helicopter to Nahrin carrying foreign and Afghan teams to coordinate the rescue effort
The World Food Programme plans to make a food delivery by helicopter
A Russian rescue team is standing by in Kabul with an Ilyushin 76 transport plane carrying 30 tonnes of medical equipment
Air transport could be vital to the relief operation, given that two of the three access roads to Nahrin are blocked.
However, food agency lorries have been successfully negotiating the area's dirt roads in recent months.
The area, where an impoverished farming community lives in mostly mud-brick homes, was already a major recipient of food aid before the quake.
The BBC Kabul correspondent, Kate Clark, notes that Nahrin suffered badly during Afghanistan's civil war and recently saw fresh ethnic violence.
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