Some people survived after fleeing initial tremors
At least 70 people have been killed and 980 injured by several earthquakes in western Iran, officials said.
The quakes, with magnitudes of up to 6.0, centred on remote villages between the industrial towns of Doroud and Boroujerd in the province of Lorestan.
About 330 villages have been damaged - some completely flattened, Lorestan's disaster control committee chief said.
Iranian President Mahmoud Ahmadinejad called for aid to be rushed to the victims, and prayed for the injured.
Setting aside political differences with Tehran, US President George W Bush offered humanitarian assistance to the victims of the quake.
Lorestan's governor said hospitals were full to capacity and he called for assistance from surrounding areas.
Ali Barani, head of Lorestan's disaster control committee, told Reuters news agency the number of casualties was not expected to rise significantly because initial tremors on Thursday night had provided a warning to residents.
The first tremors, with magnitudes of 4.7 and 5.1, hit at about 0105 on Friday (2135 GMT on Thursday), the official Irna news agency reported.
Many villagers fled their houses in fear and set up tents outside for the night.
Telephone lines, electricity and gas supplies had been cut in some areas, Doroud's governor told Irna.
Iranian television pictures on Friday showed images of flattened houses, with residents scrabbling through rubble with their bare hands.
RECENT MAJOR IRAN QUAKES
21 Feb 2005: 612 die when 6.4 magnitude quake hits Zarand, Kerman province
26 Dec 2003: 40,000 killed when 6.7 magnitude quake devastates Bam
10 May 1997: 7.1 magnitude quake kills more than 1,500 near Afghan border
28 Feb 1997: 5.5 magnitude quake kills about 1,000 in north-western Iran
21 June 1990: About 40,000 killed by 7.7 magnitude quake. Caspian regions of Gilan and Zanjan devastated.
11 June 1981: 6.8 magnitude quake destroys town of Golbaf, killing more than 1,000
"We are afraid to get back home. I spent the night with my family and guests in open space last night," Doroud resident Mahmoud Chaharmiri told the Associated Press news agency by telephone.
There were also reports of quakes in the cities of Arak and Shazand in the central Markazi province, but no casualties or damage were reported.
In a message issued after the earthquakes, the president said the nation was "deeply moved by the killer quakes in the cities of Doroud and Boroujerd which took the lives of many civilians".
"It is imperative to mobilise all the existing facilities to assist the injured civilians and address their needs immediately," he said.
"We obviously have our differences with the Iranian government but we do care about the suffering of Iranian people," President Bush said during a visit to Mexico.
The US offered to provide temporary shelter, blankets, plastic sheeting, hygienic goods and water units, State Department spokesman Adam Ereli said.
Experts say the earthquake is moderate in scale; in the past such tremors have killed thousands in rural areas of Iran, where houses are built with brick and often poorly constructed.
Iran straddles a major geological fault line and is regularly struck by powerful earthquakes.
Some 40,000 people died when the ancient city of Bam was levelled by an earthquake in December 2003.
In February 2005, more than 600 people died in a 6.4 magnitude quake centred in a remote area near Zarand in Iran's Kerman province.
Another powerful quake hit Kerman in November 2004, killing 400.