A powerful 7.3 magnitude earthquake near the Iraq-Iran border has killed more than 400 people across both countries.
Iran's western Kermanshah province bore the brunt of the quake on Sunday night, with authorities saying the quake killed 407 people in the country and injured 6700.
In Iraq, the shallow earthquake killed at least seven people and injured 535, all in the country's northern Kurdish region, according to Iraq's Interior Ministry.
The quake was centred outside the eastern Iraqi city of Halabja, according to the most recent measurements from the US Geological Survey.
It could be felt on the Mediterranean coast, some 1000 kilometres away.
Iranian social media and news agencies showed images and videos of people fleeing their homes. More than 100 aftershocks followed.
The quake's worst damage appeared to be in the town of Sarpol-e-Zahab in Kermanshah province, which sits in the Zagros Mountains that divide Iran and Iraq.
Sarpol-e-Zahab residents said the power and water were out and telephone and cellphone lines were spotty.
Iran's Supreme Leader Ayatollah Ali Khamenei offered his condolences on Monday morning and urged rescuers and government agencies to do all they could to help those affected, state media reported. President Hassan Rouhani is scheduled to tour earthquake-damaged areas on Tuesday.
The semi-official ILNA news agency said at least 14 provinces in Iran had been affected by the earthquake.
In Iraq, Prime Minister Haider al-Abadi issued a directive for the country's civil defense teams and "related institutions" to respond to the natural disaster.
The quake could be felt across Iraq, shaking buildings and homes from Irbil to Baghdad, where people fled into the streets of the capital.
The Iraqi city of Halabja, closest to the epicentre, was the target of a 1988 chemical attack in which Saddam Hussein's troops killed some 5000 people with mustard gas - the deadliest chemical weapons attack ever against civilians.
Turkey dispatched emergency aid to northern Iraq as officials expressed their "deep sadness" at the tragedy. Prime Minister Binali Yildirim said his country took immediate action to provide medical and food aid to northern Iraq.
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. The last major casualty earthquake in Iran struck in East Azerbaijan province in August 2012, killing over 300 people.