Most of the deaths reported have been in Iran, though seven people are reported to have died in the Kurdish region of northern Iraq.
Around 100 of the dead are believed to be from one town in Iran’s Kermanshah province, the country’s semi-official Mehr news agency reported on Monday.
Iran: 336 people confirmed dead, 3,950 injured, state-run IRINN TV has reported
Northern Iraq: 7 people dead, 300 people injured in the semi-autonomous Kurdish region, Rekawt Hama Rasheed, the health minister of the Kurdish Regional Government said.
Rescue efforts: Authorities in Iran and Iraq have initiated rescue operations; Iran has declared three days of mourning.
The earthquake hit late Sunday night with the epicenter across the Iraq-Iran border.
The quake, which reached a depth of 23 km (just over 14 miles) according to the US Geological Survey, was felt across the region with aftershocks hitting Pakistan, Lebanon, Kuwait and Turkey, news agencies in those countries reported.
Iraq’s Meteorological Organization issued a warning on Iraqi State TV urging citizens to stay away from buildings and to refrain from using elevators.
Iraqi Prime Minister Haider al-Abadi tweeted Monday that he “instructed civil defense teams and health and aid agencies to do all that they can to provide assistance” to those affected by the quake.
Meanwhile in Iran, the country’s Supreme Leader Ayatollah Seyyed Ali Khamenei sent a message of condolence and urged military and civilian help to be dispatched to quake victims.
Iran’s Revolutionary Guard were reportedly traveling to the affected areas to help with rescue efforts, according to Iran’s semi state-run Tasnim news agency.
In Iraq’s semi-autonomous Kurdish region four people were killed in Darbandikhan, where a dam was hit by falling rocks. Rahman Shikhani, the head of the Darbandikhan Dam told CNN that cracks were spotted in the upper part of the structure but there was no water leakage.
Meanwhile over 300 people were injured in the region, though most of these were minor, Rekawt Hama Rasheed, the health minister of the Kurdish Regional Government, said.
Majida Ameer, who lives in the south of Baghdad, said she ran to the streets with her three children after the quake hit late Sunday.
“I was sitting with my kids having dinner and suddenly the building was just dancing in the air,” Ameer told Reuters.
“I thought at first that it was a huge bomb. But then I heard everyone around me screaming: ‘Earthquake!'”
Iran sits on a major fault line between the Arabian and Eurasian plates and has experienced a number of earthquakes in the past.
The most deadly this century occurred in 2003 when a magnitude 6.6 earthquake struck the city of Bam in the south east of the country, killing some 26,000 people.
Over a decade earlier in June 1990, an estimated 37,000 people were killed and the northern cities of Rudbar, Manjil, and Lushan were destroyed along with hundreds of villages.
In 2005 a 6.4 magnitude earthquake rocked the city of Zarand in the southeastern province of Kerman, killing at least 400 people, and in 2012 a pair of earthquakes jolted northwest Iran, killing at least 300 people.