Thousands of desperate civilians were fleeing fighting Sunday on the new front opened by Iraqi forces against the Islamic State group south of the city of Mosul.

Families crammed in the back of pickup trucks, sometimes bringing dead and wounded with them, emerged from the dust after crossing the front line and were met by Kurdish forces.

Iraqi army troops and allied paramilitary fighters on Thursday launched a major offensive aimed at retaking the northern Nineveh province, the capital of which, Mosul, is the main hub of IS in Iraq.

The forces have been advancing from their base in Makhmur towards the town of Qayyarah, about 60 kilometres (35 miles) south of Mosul.

Growing numbers of civilians have been fleeing the advance to Makhmur where they are being assisted by Kurdish peshmerga forces.

"So far we have received around 3,000 people and the numbers are growing every day," Ali Khodeir Ahmed, a member of Nineveh's provincial council, told AFP in Makhmur.

"But there are no services offered to them by the Iraqi government, we have to put them up in a stadium in Makhmur," he said.

The Iraqi government has described the advance as the first phase of what is expected to be a long and difficult operation to retake Mosul, the country's second city and the largest urban centre in IS's cross-border "caliphate".

In the desert west of Makhmur, dust storms were whipped up by the line of vehicles fleeing IS-held territory, including a pickup carrying four women and 10 children in the back.

- 'Entire families have died' -

A bearded man in a yellow dishdasha traditional gown emerged from the dust, holding the body of a young girl wrapped in a blanket.

"She is dead, she is dead," he cried, his face caked in dust.

His daughter, whose back was riddled with shrapnel when shells rained down on their escape, was covered in blood.

"Some entire families have died," the father said.

The battle has so far focused on four villages west of Makhmur. Qayyarah, an area that includes a former air base and an oil facility, lies to the west, on the other bank of the Tigris River.

Smain Nuweis fled the village of Kharbardan with his family of seven squeezed into the back of his Opel.

"We have seen a lot of suffering," the 28-year-old said. "And it got worse now with the shelling."

"Daesh will not allow the people to flee, they want them to stay," said Nuweis, using an Arabic name for IS.

The provincial council official urged the government to do more for the flow of displaced people, who were given little more than water upon reaching the peshmerga.

"We need to open camps and provide urgent assistance. These people's situation is very bad, they were barely able to take any belongings with them," said Ali Khodeir Ahmed.

More than 3.3 million people have been displaced by conflict in Iraq since the start of 2014, according to figures from the United Nations.

IS seized control of large parts of Iraq in 2014, with Iraqi forces collapsing in the face of a lightning advance. Backed by a US-led coalition, Iraq has been clawing back territory from the jihadists in recent months.