Tens of thousands of civilians have fled from the southern Idlib region in northwestern Syria to the north of the province amid heavy bombardment this week, the UN humanitarian agency said Friday.

"Following the intensification of air strikes and shelling since 16 December in southern Idlib, tens of thousands of civilians are reportedly fleeing from Maaret al-Numan area in southern Idlib governorate to north," OCHA said, adding that thousands more are waiting for the bombardment to ease so that they can leave.

OCHA's statement came as the Syrian Observatory for Human Rights on Friday said clashes between Syrian regime forces and armed groups in Idlib, the country's last major opposition bastion, had killed more than 80 people in the past 24 hours.

The Observatory also reported that warplanes from Syrian regime ally Russia pounded areas around Maaret al-Numan and the nearby town of Saraqeb with a series of air strikes.

The flare-up triggered a wave of displacement from nearby areas, said an AFP correspondent in Maaret al-Numan.

OCHA said a shortage of fuel for private vehicles is limiting the movement of civilians while roads leading out of the town are "extremely dangerous" as they are reportedly being hit by air strikes.

Syrians carrying their belongings have been fleeing the southern Idlib region toward the north amid heavy bombardment
Syrians carrying their belongings have been fleeing the southern Idlib region toward the north amid heavy bombardment AFP / Aaref WATAD

"Since the evening of 19 December, residents of Maaret al-Numan town... began to communicate to the humanitarian community that they wanted to move to safety, but were unable to move due to the heavy aerial bombardment," the UN agency said.

"The numbers of families who already fled in the past 72 hours are estimated to have reached tens of thousands and there are thousands of others who are potentially waiting for the air strikes and bombardment to ease to allow them safety to move," it added.

According to OCHA there were about 163,000 people in and around Maaret al-Numan, and "hundreds of families are reported to have fled north" on Friday alone.

The Idlib region, which is home to some three million people including many displaced by Syria's civil war, is controlled by the country's former Al-Qaeda affiliate Hayat Tahrir al-Sham.

Pro-government forces launched a blistering offensive against the region in April, killing around 1,000 civilians and displacing more than 400,000 people from their homes.

Since August, the area has supposedly been protected by a ceasefire announced by Moscow, but the regime of President Bashar al-Assad has repeatedly vowed to retake the area and the Observatory says deadly bombardment and skirmishes have persisted.