A severe earthquake measuring 6.0 degrees on the Richter scale has struck northern and western Iran killing more than 500 people and injuring at least 2,000.
State media are reporting around 12,000 people are now homeless while the number of casualties is "rising".
The quake hit the city of Bouynzahra, in northwestern Qazvin province, at 4 a.m. (Irish time), and was followed by 21 aftershocks, three of which exceeded 4.0 degrees in intensity.
Shockwaves from the tremor could be felt in the capital, Tehran, 125 miles to the east.
"With every moment that passes, the number of casualties rises," said local official Mr Amir Zaherkhani. The 12,000 homeless counts only residents in the Avaj and Abgarm areas of Bouynzahra, he added.
Six villages in the Bouynzahra district were "completely destroyed," state newsagency IRNA said earlier. A total of 52 sub-districts in Avaj had suffered damage of between 50 and 100 percent, state television said.
When the injury count in Avaj had stood at only 120, officials said hospitals in the area were already full. According to Mr Zaherkhani, aid workers were now running short on tents for the wounded and homeless.
"The number of injured people is very high; exact figures are still not available, but there will be many casualties," said Mr Majid Shalviri, who heads the Red Crescent society in Qazvin, one of eight provinces shaken by the disaster.
Also hit were the western Hamedan province, Tehran province, Central province, the northern Gilan and Ardebil provinces and the western Zanjan and Kordestan provinces, state television said.
"Inhabitants in the affected areas are horrified," IRNA said. State television broadcast the first images of the affected areas Saturday afternoon, showing dust-covered inhabitants in the Avaj district of Bouynzahra. The residents were crying and kneeling on the ruins of their houses.
Most footage showed buildings and homes which had been entirely destroyed, with personal belongings strewn amid the rubble.
It also broadcast images of ruins in the western Hamedan province, where three people were said to have been killed and more than 100 others injured.
An official at Iran's seismological institute, who asked not to be identified, said province officials were being warned about the threat of more aftershocks.
"We have called on them to evacuate inhabitants in areas most at risk from suffering... further quakes," he said.
The tremor was felt strongly throughout Tehran, Iran's 10-million strong capital, moving furniture and breaking china, especially in the northern residential district of Farmanieh.
President Mohammad Khatami, who expressed his condolences to the nation, has called on officials to "co-operate with each other in order to be able to provide swift help to the victims," state radio said.
Iran is one of the most quake-prone regions in the world, with almost daily tremors.
The extent of damages are often increased by the weak structure of buildings, while relief efforts are generally hampered by badly built roads.
Today's catastrophe comes nearly 12 years to the day after the June 21, 1990 earthquake, measuring 7.6 on the Richter scale, that shook Iran's northern Gilan province. Roudbar, the location of its epicentre, was also affected by today's quake.
The Gilan quake left 37,000 people dead and more than 100,000 injured, with three cities and 600 villages completely destroyed.
AFP