Iranian state TV said Iraqi officials had reported six deaths and 200 injuries inside Iraq, though there was no official comment from Iraq's government.
The US Geological Survey said the quake was centered 31 kilometers outside the eastern Iraqi city of Halabja.
The Islamic Republic of Iran News Network quoted the head of the country's emergency medical services, Pirhossein Koulivand, as saying early Monday that at least 61 had been killed and 300 injured on Iran's side of the border.
Koulivand earlier told a local television station that the earthquake knocked out electricity in Iran's western cities of Mehran and Ilam. He also said 35 rescue teams were providing assistance.
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Iranian President Hassan Rouhani in a phone call with the Interior Ministry emphasized the need for maximum effort from officials.
Iranian social media was abuzz Sunday night with posts of people evacuating their homes, particularly in Kermanshah and Ghasr-e Shirin.
Iran sits on many major fault lines and is prone to near-daily quakes. In 2003, a magnitude 6.6 earthquake flattened the historic city of Bam, killing 26,000 people.