Christian families have abandoned their homes and fled Mosul after the Sunni rebel group, the Islamic State, threatened them with death if they did not convert to Islam or pay tax.

"Some families have had all their money and jewellery taken from them at an insurgent checkpoint as they fled the city," Abu Rayan, a Christian who left Mosul with his family told AFP news agency on Saturday.

"Some of our homes have already been confiscated and I know families who have handed their keys to neighbours, asking them to look after their property with the hope they would return one day." Rayan said.

The hardline group on Friday ordered Christians in Mosul that they could convert, pay a tax or flee the city after abandoning their possessions.

An earlier Islamic State statement said there would be "nothing but the sword" if Christians did not abide by those conditions by 9am GMT on Saturday.

The AFP said that hundreds of Christians had fled by the deadline, although Al Jazeera could not confirm these numbers.

While some families initially appeared prepared to pay the "jizya" Islamic tribute to stay in their ancient homes, messages broadcast by mosques on Friday appeared to spark an exodus.

"Christian families are on their way to Dohuk and Arbil" in the autonomous Kurdish region of Iraq, 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," he said, putting the number of those who were still in the city 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.

The mass displacement was the latest in 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.