In the early hours of Tuesday September 26, hundreds of men, women and children were making a perilous trek through the Syrian desert by night.

After weeks of trying, they had finally managed to escape a small Islamic State-held pocket in Syria's Hama province near the town of Oqeirbat.

They were attempting to make their way across regime-held territory and into rebel held north-western Syria.

Families walked for hours, guided by the stars and the moon in the dark. Across harsh desert terrain, carrying small children and the few belongings they had.

Sheep and goats were sent ahead, in case there were any landmines.

Suddenly, the hundreds of men, women and children came under fire.

According to survivors, dozens — perhaps 70-80 people — may have been killed in the incident.

"I was walking with a group of almost thirty people," 22-year-old survivor Khaled Abu Mariam said.

"Only me and another person survived."

The families were trying to cross from an IS controlled area (grey) to the rebel held north (green). The attack purportedly happened in regime-controlled territory (red). ( ABC News: Sophie McNeill )

Mr Abu Mariam, who spoke to the ABC from a camp where he and other survivors are now sheltering in Western Aleppo, said he believes the fleeing families were hit with machine guns and tank shelling from Syrian government forces.

"We made it to the main road, we were in a location between two Syrian army checkpoints. And we were fired at from both sides," he said.

Another survivor, Mnahi Al Ahmad, said it was impossible to know the exact number killed or injured because it was dark and people had rushed away, leaving the dead behind.

Adding to uncertainty about the full toll, the families walked in separate groups. Most seemed to know only of their own dead.

The ABC was sent phone video interviews with other survivors who were now in a camp for displaced families in Western Aleppo.

"We were running away, I saw around six or seven die and before that another seven out of around fifteen in my group. Many of them were women and children," one man said in the video.

"The valley was full of people, they were shelling us," another woman added.

"We were massacred there; people were dying on the ground."

Survivors say it is impossible to know how many died because the attack came upon them at night. ( ABC News: Sophie McNeill )

The survivor accounts match up with information received by UN officials in Damascus who say they received reports of the attack from two different sources.

"A large number of people were trying to flee from one area to another," a UN official said.

"That's when they were reportedly hit, resulting in a large number of people being killed."

The UN official said they had received reports that between 70-80 people had been killed and that the attack had taken place in regime-controlled territory.

The Syrian Network for Human Rights told the ABC it hasn't been able to determine the exact number of victims due to the remote nature of where the attack occurred.

Yasser Mohamad, a volunteer with the Saed Charity which works in opposition-controlled territory, said he met survivors from the incident when his team arrived to do a mobile clinic in the camp they are now sheltering in.

"Some of the children arrived at the camp alone, with no parents," Yasser Mohammad told the ABC.

"The children were suffering from malnutrition and the women were suffering from having walked for long hours."

The survivors in the camps said they had tried to escape the IS controlled area near Oqeirbat in early September but it had proven too dangerous.

Mr Mohamad spoke of one little girl, Tayba, who survived last week's incident but who lost her parents and her arm in early September when families had first tried to escape.

"She lost her left arm and the woman who brought her to us told me her parents were killed," he said.

One woman shakes her fist angrily as she speaks about her two daughters she says were killed in the first attempt to escape.

"One was 12 years old and one was nine years old," she yells.

"They were killed by the Russian jets, we gathered their body parts, the fragments, off the ground."