The UN refugee agency, UNHCR says some 900 people have fled the Iraqi city of Mosul and crossed the border into Syria.
This is the first large group of civilians confirmed to have escaped since Iraqi forces began its offensive to liberate Mosul from the Islamic state on Monday.
As many as 1.5 million people are thought to be in Mosul, with up to 5,000 IS fighters.
This has prompted fears that the militants will use the civilians as human shields by moving into their neighbourhoods as Iraqi forces get closer to Mosul.
Since Mosul’s capture by ISIS fighters in June 2014, Mosul has been a vital stronghold for ISIS.
It is the largest city under ISIS control in Iraq and Syria and it was the city from which the group first declared the establishment of its so-called caliphate.
Mosul residents had been told by the Iraqi government that it may be safer to stay in the city while the operation is under way – with fears that the militants have booby-trapped roads and placed snipers on routes, in and out.
The UN however says it is working to create new refugee camps to the south, east and north of Mosul, as it predicts about 200,000 people will need shelter in the first days and weeks of the operation.