The Irish Government has pledged up to €1 million to assist earthquake victims. Minister of State for Development Co-operation and Human Rights Tom Kitt said the funding will be channelled primarily through the Red Crescent organisation and other humanitarian agencies including the UN.
Survivors and rescue teams were struggling in sub-zero temperatures to find anyone still alive under the rubble that was, until the early hours, the bustling city of Bam.
Official figures said 6,000 people were killed and 30,000 injured most of them critically in the south-eastern city.
But Iranian MP Hasan Khoshrou said that 10,000 had been killed and other officials doubled that figure.
He said people at the scene had told him the devastation was "beyond imagination".
The government said 70% of houses in the city of 80,000 people had been destroyed.
A Turkish TV reporter in Bam said it looked at if the city had been bombed.
Thousands who survived were left homeless and were spending the night in the open in freezing weather.
The Iranian government asked for international assistance particularly search and rescue teams.
The 6.3-magnitude quake hit Bam, 630 miles from the capital Tehran, at 5.28am (1.58am Irish time). "The quake hit the city when most of the people were in bed, raising fears that the death toll may go higher," said Mr Khoshrou.
Hardly a building remained upright in the old quarter of Bam. In one street, only a wall and the trees were standing. Mohammad Karimi, in his 30s, lost his wife and four-year-old daughter.
"This is the day of resurrection. There is nothing but devastation and debris," he said as he held his dead daughter in his arms. "Trucks are hauling bodies to bury them in mass graves."
President Mohammad Khatami attended an emergency meeting and urged the entire country to help the victims of the quake. He declared three days of mourning for what he called a "national tragedy".
The government told the UN it needs medicines, tents and generators. Because hospitals in the area had been destroyed, the government sent transport planes to evacuate the wounded for treatment elsewhere.
Interior Minister Abdolvahed Mousavi Lari said 70% of residential Bam had been destroyed and there was no electricity.
"Our immediate two priorities are dealing with the people who are trapped and transferring the wounded to other areas," he said. He said four C-130 Hercules transport planes had ferried wounded out of the area.
Mr Mousavi said setting up tents was a priority because of the cold night-time temperatures were expected to drop to minus 6C (21F) and the large-scale destruction of buildings.
The governor of Kerman province, Mohammad Ali Karimi, said: "The death toll is very high.
"Many people are buried under the rubble," he said. "We do not have any precise information. What is certain is that the old structure of the city has been totally destroyed."
Hardly any buildings in Iran are built to withstand earthquakes, although the country sits on several major fault lines and tremors are frequent.
About 500 people were evacuated to hospitals in Kerman, where they were in critical condition, officials said.
Many injured lay on the floor as doctors attended to more critical patients.
Bam's two hospitals were reported to have been destroyed by the quake.
Iran's Health Ministry appealed to international organisations to fly in aid. Ministry official Mohammad Ismail Akbari said the priority requirements were disinfectants, equipment to test if water is contaminated, water pumps and electricity generators.
Iran's Red Crescent, the Islamic equivalent of the Red Cross, said rescue and relief teams had been sent to Bam from numerous provinces.
The oldest part of the city dates to about 2,000 years ago, but most was built in the 15th to 18th centuries.