The United Nations (UN) on Thursday estimated that thousands of people still remain in eastern Aleppo as evacuations escorted by the Syrian Arab Red Crescent (SARC) and the International Committee of the Red Cross (ICRC) continued overnight and throughout the day in the besieged northern Syrian city, a UN spokesman told reporters.

"While operations are ongoing, the evacuation is believed to be in its final stage," Farhan Haq, the deputy UN spokesman, said at a daily news briefing here, China's Xinhua news agency reported.

"The UN estimates that thousands more remain in eastern Aleppo enclaves," Haq said.

Since Wednesday night, UN monitors at the Ramouseh government checkpoint in Aleppo observed thousands of people departing from eastern Aleppo mainly in private vehicles that struggled to advance due to a snow storm and sub-zero temperatures, Haq said.

Overall, ICRC estimates that more than 34,000 people have been evacuated from the besieged neighbourhoods in eastern Aleppo since Dec 15.

According to the World Health Organisation (WHO), as of Dec 21, 435 wounded and sick had been evacuated, of whom 95 patients in critical conditions had been transferred to Turkey, others were transferred to hospitals in Idlib and in rural western Aleppo, Haq noted.

"Protection of civilians leaving these areas remains the biggest concern," he said. "The process for evacuation was traumatic, with crowding, and vulnerable people waiting for hours and exposed to sub-zero temperatures."

"All remaining civilians must be allowed to safely leave should they choose to do so," he said. "Access to people in need to provide them with life-saving humanitarian assistance is also urgently needed."

The evacuation is part of a deal concluded recently between Russia and Turkey, Xinhua reported.

It included the evacuation of civilians from the Shiite towns of Kafraya and Foa, which are besieged by the rebels in the northwestern province of Idlib.

It came as the Syrian army was on a crushing offensive against the rebel-held part of Aleppo, which resulted in wresting back control over 99 per cent of eastern Aleppo.

The evacuation operation has been ongoing since last Thursday, and the rebels were leaving in buses and cars through the Ramouseh crossing south of Aleppo toward rebel-held areas in the southwestern countryside of Aleppo. - Bernama