Air strikes killed dozens of civilians in Eastern Ghouta and forced thousands to flee their homes Friday as Syrian and allied forces pressed their blistering assault on the six-year-old rebel stronghold.

At least 76 civilians were killed as the toll for the month-old assault near Damascus continued to mount and world powers remained unable to stop one of the seven-year conflict's worst crises.

The war entered its eighth year with another deadly assault unfolding in the north, where Turkish-led forces pressed an operation to seize the Kurdish-majority region of Afrin, sending thousands more civilians on to the roads.

Turkish artillery fire killed 27 civilians on Friday in the city of Afrin, where remaining residents were stocking up on food in preparation for a fully-fledged siege.

On the edge of Ghouta, a sprawling semi-rural area within mortar range of central Damascus, hundreds of civilians were still streaming out of destroyed towns, carrying scant belongings in bags and bundles.

Exhausted and distraught, the estimated 40,000 people who poured out of Ghouta on Thursday had harrowing tales of life in fear and deprivation, trapped for weeks in their cellars as regime and Russian jets rained bombs.

"We were around 66 families in the basement, with seven people per family," Hussein Samid told AFP, pausing on the roadside to smoke a cigarette.

"Those of us who were in the cellar got together and decided to leave, whatever the cost," the 40-year-old said.

- Exodus -

Hundreds of them were crammed in a centre on the edge of Eastern Ghouta on Friday, unsure what the next step would be after walking straight into the arms of the forces that have relentlessly pounded their homes for weeks.

They were sitting on the ground and had little access to sanitation as the sudden exodus appeared to have caught the government flat-footed.

Despite mild temperatures, most of them were wearing several layers of heavy winter clothes, the same they had kept on for weeks in their freezing basements.

The Syrian army in a message broadcast on state television urged all residents to use "corridors" to leave the enclave as it claimed to have recaptured 70 percent of rebel territory.

The ground offensive pressed by Syrian troops and allied militia has splintered Eastern Ghouta into three pockets.

Most of the civilians fleeing since Thursday have left from the town of Hammuriyeh, in the south of Eastern Ghouta.

The Islamist and jihadist groups which have dominated this area of the enclave over the past few years retook much of the town they had almost lost a day earlier, the Syrian Observatory for Human Rights said.

"Hayat Tahrir al-Sham and Faylaq al-Rahman have almost completely retaken the town but fighting continues on the outskirts," the Britain-based monitoring group said.

Few residents remain in Hammuriyeh itself but tens of thousands of others were still scattered across the southwestern pocket, the largest of three still in rebel hands.

President of the International Committee of the Red Cross Peter Maurer, who was inside rebel-held Ghouta on Thursday when food aid was brought in, voiced his exasperation with the continued bloodshed.

"I am myself with many humanitarian workers on the ground both exhausted and fed up with the blind justification of gross violations against civilians," he said in a statement.

- Afrin encircled -

The Observatory said at least 76 civilians were killed in Russian air strikes on the southwestern Ghouta pocket on Friday.

More than 60 died in Kafr Batna, where the Observatory said incendiary weapons were used.

The latest deaths brought to more than 1,330 the number of civilians killed since the start of the ground and air offensive on the enclave on February 18, around a fifth of them children.

Syrian President Bashar al-Assad has in recent months recovered swathes of territory lost at the beginning of the conflict and Ghouta was one of his key remaining targets.

An exodus of similar proportions was under way hundreds of kilometres (miles) to the north near the border with Turkey, as civilians tried to escape a looming siege of the city of Afrin.

The Observatory said on Thursday that more than 30,000 people had fled the city of Afrin in 24 hours and civilians were still trying to slip out on Friday before Turkish-led forces cut the last exit road.

The UN said it was worried the forces staying inside were reluctant to allow civilians to flee, as that would leave them even more exposed to Turkey's vastly superior firepower.

Ravina Shamdasani, spokesperson for the UN's Rights Office decried "reports that civilians are being prevented from leaving Afrin city by Kurdish forces ... (and) are being held to be used as human shields."

The death toll also mounted in Afrin, with the latest Turkish artillery fire killing 22 civilians, seven of them children, according to the Observatory.

On January 20, Turkey and Syrian Arab rebel proxies launched an air and ground offensive on the Afrin region, which is controlled by the US-backed Kurdish People's Protection Units (YPG).

In seven years, more than half of Syria's pre-war population of 20 million has been displaced.