Tens of thousands of Syrian civilians have fled ferocious fighting between Russian-backed regime forces and Islamic State group jihadists over the past week in the country's ravaged north, AFP reports.

Supported by Russian air power and artillery, Syrian government forces have waged a fierce offensive against IS, seizing around 90 villages from the jihadists since mid-January.

Their aim, according to the Syrian Observatory for Human Rights monitoring group, is IS-held Khafsah, the main station pumping water into Aleppo.

Residents of Syria's second city have been without mains water for 47 days after the jihadists cut the supply.

The fighting over the past week has sparked an exodus of "more than 30,000 civilians, most of them women and children," Observatory head Rami Abdel Rahman said Saturday, March 4.

Most of the displaced went to areas around Manbij, under the control of the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters backed by the United States that is also fighting IS, the monitor said.

An AFP correspondent in Manbij saw dozens of displaced families speeding towards the relative safety of the town on motorcycles and in small buses and cars.

Many of them looked exhausted as they lined up at a checkpoint manned by the Manbij Military Council, the SDF unit that controls the town, to be searched and get permission to enter.