Two strong earthquakes have struck north-western Iran, leaving at least 180 people dead and more than 1,300 injured, officials say.
The quakes struck near Tabriz and Ahar, but most of the casualties are thought to be in outlying villages.
Six villages were destroyed, and thousands are spending the night in emergency shelters or in the open.
Another 60 villages sustained more than 50% damage, and the death toll is expected to rise.
Reports say phone lines to many villages have been cut off, making rescue efforts harder.
The US Geological Service measured the quakes at magnitude 6.4 and 6.3.
The first tremor occured at 16:53 local time (12:23 GMT), according to state TV.
"The quake has created huge panic among the people," one resident of Tabriz told the BBC. "Everyone has rushed to the streets and the sirens of ambulances are everywhere."
The towns of Haris and Varzaqan in East Azerbaijan province were among those that suffered casualties, Khalil Saei, local crisis committee chief, told state TV, according to the Associated Press.
'My family is terrified'
Dozens of rescue workers have been sent to the region, but relief efforts have been limited overnight. Phone communication in the city of Tabriz has also been disrupted, reports say.
An Iranian Red Crescent official estimated that 16,000 people have been given emergency shelter after they were forced to leave their homes.
President Mahmoud Ahmadinejad's office posted a statement on its website expressing condolences to those in the disaster zone and calling on authorities to "mobilise all efforts to help the affected populations," the AFP news agency reports.
A provincial official has warned people in the region to stay outdoors overnight because of the risk of aftershocks.
"My family is really terrified. It is night time now but we cannot sleep," Tabriz resident Amina Zia told the BBC.
"This earthquake was... very strong and violent.
"There were around 10 aftershocks, which lasted a total of 10 minutes."
The two earthquakes came within minutes of each other, according to seismology experts at Tehran University.
Iran straddles a major geological fault like, making it prone to seismic activity. In 2003 an earthquake in the city of Bam left 25,000 people dead.