By Jomana Karadsheh, Kareem Khadder, Tamara Qiblawi and Sarah Sirgany, CNN

(CNN) -- Thousands of people fled the besieged area of Eastern Ghouta on Thursday as Syrian forces advanced into the rebel-held enclave on the edge of Damascus, state TV and monitoring groups reported.

The Syrian news agency SANA said more than 10,000 had escaped from the town of Hamoriya to government-controlled parts of the Syrian capital. The UK-based Syrian Observatory for Human Rights (SOHR) put the figure at more than 12,500.

Images on state TV showed hundreds of people carring their belongings out the enclave on foot and in the back of pickup trucks. Soldiers were seen in the footage, but there were no signs of local or international aid groups.

The Red Cross told CNN they were not involved in the ongoing exodus -- one of the largest in a single day during Syria's war, which entered its eighth year on Thursday.

The UN children's agency said it was assisting families and children at three shelters in suburban Damascus and at reception points outside the enclave. The civilian exodus comes hours after reports of intensified overnight airstrikes in Eastern Ghouta.

One of Eastern Ghouta's major rebel groups, Faylaq al Rahman, withdrew from Hamoriya as the Syrian military moved rapidly into the town, according to SOHR.

A Faylaq al Rahman spokesman CNN spoke to declined to say whether the group had pulled out, but accused Syrian regime forces of using escaping civilians as human shields during their advance.

The scenes are reminiscent of the mass evacuations that occurred when regime troops overran Aleppo in a brutal military campaign in 2016. That battle was considered one of the bloodiest of Syria's civil war.

A matter of time

Eastern Ghouta has been under siege since 2012, but a renewed government assault that began in mid-February has left more than 1,000 civilians dead.

The Syrian government has advanced steadily into Eastern Ghouta, starting with villages and towns in the east before regime forces split the rebel-held areas of the suburb into three parts last week.

The offensive has been carried out with the support of Russia, a key ally of Syrian President Bashar al-Assad, and in defiance of a United Nations call for a ceasefire.

Observers say it is now only a matter of time before the regime takes control of the entire enclave, one of the last major rebel-held areas in the country.

"This is the horrifying aspect of this. We could see all of this weeks ago that it was going to happen," said Center of British Arab Understand directory Chris Doyle. "An endless amount of suffering could have been avoided with some sort of sensible deal."