Their escape from jihadist rule was gruelling and their new living conditions hardly better, but the Iraqis fleeing south of Mosul are only the first of a feared massive exodus.

Qayyarah is not only the main staging base for the huge offensive Iraqi forces launched to retake Mosul on October 17 -- it is also where displaced families in the area are converging.

"We walked all night to escape the jihadists and just before arriving here, our neighbours were killed in a bomb blast," said Umm Mahmud, a woman from Hawijah.

Her town lies in an area near Kirkuk on the other bank of the Tigris river and is one of the last bastions of the Islamic State group that took over swathes of Iraq in 2014 and declared an Islamic "caliphate".

She and her family fled to Qayyarah, an area recaptured from the jihadists a few weeks ago and which is now the main hub behind the southern lines of the Mosul battlefield.

There she joined the growing number of people who are fleeing the fighting and two years of brutal jihadist rule, travelling in the opposite direction to thousands of forces battling their way northward to Mosul.

"An IS member helped us flee. He asked for $100 per person to take us to a nearby village," said the woman.

They were then left alone to trek through a minefield planted by the jihadists, she said.

Only slightly more than 5,000 people are believed to have fled their homes since the start of the offensive a week ago, but the United Nations believes that more than a million people are still trapped inside Mosul.

When Iraqi forces get closer to the boundaries of the city, aid groups expect a huge outflow of civilians which they fear existing infrastructure simply will not be able to handle.

The Jedaah camp in Qayyarah is run by the authorities of Nineveh province, of which Mosul is the capital.

- Food shortages -

It opened on October 19 and is supported by aid groups and the UN's Children Fund.

A few kilometres (miles) north, the fleeing families are screened at a checkpoint manned by the Iraqi security forces who were herding the newly displaced residents towards Qayyarah.

They left their homes for various reasons, some of them to avoid being caught in clashes between advancing federal forces and die-hard IS fighters.

Others left because of dwindling food supplies.

"If you're with IS you get everything you need. But the others have nothing to eat because of the blockade," one of the recently arrived told AFP.

Dozens of civilians huddled together near the camp which was littered with trash, as wind blew in clouds of smoke from burning oil wells and a fire at a nearby sulphur plant.

Most of them escaped the "caliphate" with just one or two bags containing some clothes and other essentials.

"The jihadists fled our village south of Mosul four days ago, slipping out from the Iraqi forces' siege under the cover of night," said Abu Jowaher, 27.

"We were left there alone, with no water or food," he said.

"Some of us decided to leave too and others stayed back to look after the sheep," he said, as an ambulance returned from the front line to the north.

A small pick-up truck followed behind full of displaced people, including one man still waving his white flag.