The line of cars flying white flags kept on coming Tuesday as Iraqi forces began to evacuate residents of the last villages near the Islamic State group bastion of Mosul.

And it was not just people. Some vehicles had animals perched on piles of blankets amid foam mattresses and plastic buckets of clothing.

Units of Iraq's elite counter-terrorism force were just half a dozen kilometres (four miles) from Mosul, where IS two years ago proclaimed its "caliphate" and which is now being targeted by Kurdish and Iraqi forces backed by the international coalition.

The advance on Mosul, Iraq's second city, has been rapid so far.

Villages emptied of their populations since the arrival of the jihadists in mid-2014 were quickly retaken.

Just a few inhabited villages lie ahead of them now, and they are evacuating the people who live there.

People like Essam Saadou, a 22-year-old student at the wheel of a car crowded with three women and two children.

"We've brought nothing with us. We took to the road despite all the dangers. We have just the car and the clothes we're wearing," Saadou told AFP at a Kurdish checkpoint where families were being put on buses to nearby camps constructed recently on the plain.

"The counter-terrorism people brought us here and handed us over to the peshmergas, and they'll take us to a camp. We will see what happens," he said.

Amal Mohammed, a 20-year-old Sunni Kurd, is sitting in the back.

She has thrown back the black face veil the jihadists made her wear after they "appeared in one day" in the village of Topzawa, near Mosul.

"They controlled our lives completely: we had to wear the niqab, the abaya (full veil and a long black robe)," she said.

- 'Everything was forbidden' -

"We couldn't go out of the house to see those closest to us. Even going upstairs to the roof terrace was not allowed," said the young mother, a baby girl asleep in her arms.

"Everything was forbidden" under IS rule, she added.

They have now been able to leave IS-controlled territory, but the ordeal of the hundreds of people waiting for hours under a burning sun Tuesday for a hypothetical transfer to a camp is far from over.

The UN refugee agency's chief said on Monday that the UNHCR would soon be ready to accommodate 150,000 people displaced by the battle for Mosul.

"The preparations are proceeding well... UNHCR is going to have in two or three days 30,000 tents in Iraq, enough for 150,000 people," Filippo Grandi told reporters in Jordan after visiting Iraq.

He said that 7,500 people have already fled the outskirts of Mosul and that around 1,000 have crossed into Syria.

Concerns are mounting for the UN-estimated 1.5 million people in the wider Mosul area.

A million people could be displaced by the assault on the city, sparking an unprecedented humanitarian emergency in Iraq which already has more than three million displaced, more than a third of them in the autonomous Kurdish areas.

Between cars at the checkpoint on Tuesday, as they kept an eye on children playing by the roadside, small groups of men, some with their heads covered with a traditional scarf, discussed the situation.

Women and children were the first to board the bus to a huge camp just a few hundred metres (yards) away, beyond the checkpoint.

The men don't yet know if they will be able to go too.