The quake struck the mountainous area of Sulaimaniyah province at 9:18 pm (local time) at a depth of 25 kilometres , the monitor said.
It was felt for about 20 seconds in Baghdad, and sometimes for longer in other provinces of Iraq, journalists said.
Many residents in the Iraqi capital Baghdad rushed out of houses and tall buildings in panic.
"I was sitting with my kids having dinner and suddenly the building was just dancing in the air,' said Majida Ameer, who ran out of her building in the capital's Salihiya district with her three children.
"I thought at first that it was a huge bomb. But then I heard everyone around me screaming 'Earthquake!'"
There were similar scenes in Erbil, the capital of the semi-autonomous Kurdistan Region, and across other cities in northern Iraq, close to the quake's epicentre.
Iraq's meteorology center advised people to stay away from buildings and not to use elevators, in case of aftershocks.
The quake was even felt in the Iranian capital Tehran, with some villages hit by power cuts, Iranian state TV reported.
"The quake was felt in several Iranian provinces bordering Iraq ... Eight villages were damaged ... Electricity has been cut in some villages and rescue teams have been dispatched to those areas," TV reported.
Residents of Turkey's southeastern city of Diyarbakir also reported feeling a strong tremor, but there were no immediate reports of damage or casualties in the city.
One person on Twitter has described building "violently shaking."
"Just survived an earthquake.
"Building violently shaking.
"Ran from 19th floor. Many tears here. Thank God, alive and out safely!"
Pictures and video shared on social media show people seeking safety in Sulaymaniyah as well of damaged buildings.
Residents of Turkey's southeastern city of Diyarbakir also reported feeling a strong tremor, but there were no immediate reports of damage or casualties in the city.
In the province of Sulaimaniyah, located in Iraq's Kurdistan region, residents ran out onto the streets at the time of the quake and some minor property damage was recorded, a reporter said.
In Iran, ISNA said the earthquake was felt in several cities in the west of the country including Tabriz.
In southeastern Turkey, the earthquake was felt "from Malatya to Van", a correspondent said. In the town of Diyarbakir, residents also left their homes before returning.
The quake took place along a 1,500 kilometre fault line between the Arabia and Eurasia tectonic plates, a belt extending through western Iran and into northeastern Iraq, the US Geological Survey said.
A 5.7 magnitude earthquake near Iran's border with Turkmenistan in May killed two people, injured hundreds and caused widespread damage, state media reported.
The last major earthquake to strike Iran was a 2003 tremor in Bam, in the southeastern province of Kerman, which killed at least 31,000 people and flattened the city.
Meanwhile in Japan, a 6.2 magnitude earthquake struck tonight.
An Iraqi meteorology official said capital Baghdad was hit by an earthquake of approximately 6.5, but it was unclear if they were referencing the same quake.
- additional reporting NZ Herald
