Thousands of Christians poured into Kurdistan as they fled a Saturday ultimatum by jihadists who overran northwestern Iraq last month and proclaimed a caliphate.
As militants attempted to break government defences in strategic areas and edge closer to Baghdad, Christians joined hundreds of thousands of Shiite and other refugees into Kurdistan.
Their flight to the safety of the neighbouring autonomous region coincided with the expected homecoming of Iraq's Kurdish president, Jalal Talabani, after 18 months of medical treatment in Germany.
The Islamic State (IS) group running Mosul had already demanded that those Christians still in the city convert, pay a special tax or leave but messages blaring on mosques' loudspeakers appeared to spark an exodus.
An earlier statement by Mosul's new rulers had said there would be "nothing for them but the sword" if Christians did not abide by those conditions before noon (0900 GMT) on Saturday.
"Christian families are on their way to Dohuk and Arbil" in Kurdistan, Chaldean patriarch Louis Sako, who heads Iraq's largest Christian community, told AFP.
"For the first time in the history of Iraq, Mosul is now empty of Christians."
Most Christians in the northwestern Nineveh province fled in terror after jihadist-led militants enforcing an extreme version of sharia -- or Islamic law -- launched an offensive on June 9.
But many of the poorest families returned when the fighting stopped and IS started administering the city. Sako put the number of Christians who were still in Mosul on Thursday at 25,000.
The Islamic State "seems intent on wiping out all traces of minority groups from areas it now controls in Iraq," Human Rights Watch said in a statement Saturday.
Other minorities rooted in the same province of Nineveh have suffered even more than the Christians, according to crimes HRW documented against the Yazidis, as well as the Turkmen and Shabak Shiite communities.
The mass displacement was the latest in six weeks of turmoil which has forced more than 600,000 people from their homes, left thousands dead and brought Iraq to the brink of collapse.
Talabani's return to his native Kurdistan Saturday was likely to spark celebrations among supporters from his Patriotic Union of Kurdistan party.
He is widely celebrated as a skilled negotiator, who enjoys good relations with both the United States and Iran and has repeatedly mediated between Iraq's fractious politicians in recent years.
But some observers warned there was little the avuncular 80-year-old head of state could do to ease spiralling ethno-sectarian violence and rhetoric and roll back the Islamic State's expansion.
"I really do think this is a post-Talabani era. I've stuck my neck out there, but I haven't heard any Iraqis talking about him in any way being president," said Toby Dodge, director of the London School of Economics' Middle East centre.
Federal forces collapsed, in some cases abandoning uniforms and weapons in their retreat, when fighters under the command of IS leader Abu Bakr al-Baghdadi launched their assault.
The army has since regrouped, received intelligence, hardware and manpower from Washington, Moscow and Shiite militias, but nonetheless struggled to regain lost territory.
Security analysts have said Baghdad remains too big a target but the militants have in recent days repeatedly attacked targets that would expose the capital if captured.
On Thursday night, a jihadist commando stormed the Speicher air base north of ex-president Saddam Hussein's hometown of Tikrit, sparking a fierce battle.
"Last night, gunmen infiltrated the base. There were snipers and suicide bombers among them, they managed to reach the runway," an intelligence officer who survived the attack told AFP.
He said the pilots managed to fly all but one of the base's aircraft to safety but a statement posted on jihadist Internet sites said many were destroyed.
Many, including within his own Shiite alliance that comfortably won April elections, now see Prime Minister Nuri al-Maliki's departure as essential to national reconciliation efforts.
In a Friday sermon delivered by one of his spokesmen in Karbala, the Iranian-born Grand Ayatollah Ali al-Sistani -- Iraq's most revered Shiite cleric -- appeared to lean in the same direction.
"The new government should have broad national acceptance and be capable of solving the crisis in the country and correcting the mistakes of the past," he said.
Parliamentary blocs have until Sunday to submit nominees for the post of president, whose election is the next step in what has been a protracted and acrimonious process to renew Iraq's leadership.
Despite his unexpected return, there is little expectation that Talabani, who has been president since 2005, will seek another term.