The government is scrambling to get aid to the worst-hit area in the mountainous province of Kermanshah, where hundreds of homes were destroyed.
More than 430 people were killed and about 7,000 injured when the quake hit near the Iran-Iraq border on Sunday.
Iran has declared Tuesday a national day of mourning.
President Hassan Rouhani is due to visit the region but international media organisations are not being allowed to visit the quake-hit areas.
Iranian state news agency Irna said 430 people had died in the country. In the more sparsely populated areas across the border in Iraq, nine people died and several hundred were injured.
Mansoureh Bagheri, an Iran-based official with the Red Crescent Society, told the BBC about 12,000 residential buildings had “totally collapsed”. She said now that rescue operations had ended, the priority was getting people into shelters as quickly as possible.
Iranian state TV said thousands of survivors had spent another night in makeshift camps or in the open. Many whose homes were still intact were frightened of returning because of dozens of aftershocks.
“It is a very cold night… we need help. We need everything. The authorities should speed up their help,” said one homeless young woman in Sarpol-e-Zahab, where most of the victims died.
One aid agency said 70,000 people needed shelter and the UN said it was “ready to assist if required”.
Maj Gen Mohammad Ali Jafari, head of the elite Islamic Revolutionary Guards Corps (IRGC), said that the immediate needs were tents, water and food.
“Newly constructed buildings… held up well, but the old houses built with earth were totally destroyed,” he told state TV while visiting the affected region.
The Iranian Red Crescent said many areas lacked water and electricity and that aid supplies were being hampered by blocked roads. Iranian army helicopters were taking part in the relief effort.
About 30 Red Crescent teams are working in the earthquake zone, the official Irna news agency reported.
Authorities said that more than 30,000 houses had been damaged and at least two villages completely destroyed.
The 7.3-magnitude quake – the deadliest in the world this year – struck at 21:18 local time (18:18 GMT) about 30km (19 miles) south of Darbandikhan, near the north-eastern border with Iran, the US Geological Survey (USGS) said.
Tremors were felt as far away as Turkey, Israel and Kuwait.
In Sarpol-e-Zahab on Monday a woman and her baby were pulled alive from rubble, Iranian media said.
The town’s main hospital was badly damaged and was struggling to treat hundreds of injured people, state TV reported. (Courtesy BBC)