 LONDON -- Civilians, some of them wounded, boarded ambulances and buses as an operation to evacuate thousands of residents from the last rebel-held enclave of eastern Aleppo got underway on Thursday.

The first 1,000 civilians, including 300 children and 28 injured, have been evacuated to Idlib, a rebel stronghold in the western countryside of Aleppo, said the International Committee of the Red Cross. Earlier, the ICRC said that 20 buses and 13 ambulances had crossed the front lines carrying civilians, including critically wounded. More civilians are to be evacuated, said the ICRC.

“We are hoping that more will be evacuated very soon,” Matthew Morris, an ICRC spokesperson, told ABC News, adding that the vehicles and buses that drove the first batch of civilians have returned to eastern Aleppo to pick up more. The process of getting all civilians out of the area could take days, he said, and around 100 ICRC and Syrian Red Crescent staff members are likely to be working overnight.

The evacuation is part of a cease-fire deal that marks the end of years of fighting and months of bitter siege in eastern Aleppo — and a strategic victory for President Bashar al-Assad, returning the last rebel stronghold in a big Syrian city to his control.

In recent weeks, the Syrian government, with help from its Russian and Iranian allies, intensified airstrikes on eastern Aleppo in an offensive that killed hundreds of civilians and displaced tens of thousands.

Some residents said they will be sad to leave their homes even though they had been living with the danger of regular bombardments and with little access to basic human needs such as food, health care, water and fuel for heating.

“People in the street — some of them are happy, maybe most of them are happy that they are going out safe. Some of them are angry they are leaving their city,” said Wissam Zarqa, a teacher who said he remains in eastern Aleppo with his family and friends. "I saw some of them crying. This is almost my feeling in a way.”

Zarqa and other residents said that some people have been burning belongings that they can’t bring with them out of the city — such as motorbikes and cars — so that they won’t be taken by forces loyal to Assad.

Evacuations had been planned for Wednesday morning but the operation was postponed after a truce between rebels and forces loyal to Assad was broken. On Wednesday, residents said that artillery shells and airstrikes pounded eastern Aleppo. The United Nations described the renewed bombardment by the Syrian government and its allies as “almost certainly a violation of international law” and most likely a “war crime.”

“I am appalled that the deal enabling the evacuation of many thousands of civilians, including the wounded and the sick, from the remaining opposition-held area of eastern Aleppo appears to have collapsed,” U.N. High Commissioner for Human Rights Zeid Ra’ad al-Hussein said on Wednesday.

On Wednesday night, rebel groups announced that a new truce was to start and that evacuations were to take place Thursday morning.

In a short clip posted to YouTube on Thursday, Assad said that “history is being made” today with the “liberation of Aleppo."