The Syrian Kurdish YPG militia said Islamic State (IS) was on the verge of defeat in Raqqa, as exhausted citizens fled the grips of the terrorist group.

Key points: US backed fighters have captured more than 80 per cent of the city

US backed fighters have captured more than 80 per cent of the city New video shows terrified residents fleeing IS-held neighbourhoods

New video shows terrified residents fleeing IS-held neighbourhoods It is estimated 4,000 civilians still remain trapped in the city

"The battles are continuing in Raqqa city. [IS] is on the verge of being finished. Today or tomorrow the city may be liberated," YPG spokesman Nouri Mahmoud said.

Some 100 IS fighters handed themselves over to US-backed fighters in the northern city as fighting continued with remaining gunmen in a pocket inside the city.

Omar Alloush of the Raqqa Civilian Council did not give details of how the 100 fighters surrendered but said fighting is still ongoing in parts of the city that was once the de facto capital of IS.

US-backed fighters of the Syrian Democratic Forces (SDF) have been on the offensive in Raqqa since early June and have so far captured more than 80 per cent of the city under the cover of airstrikes by the US-led coalition.

IS still controls the city's stadium that is believed to be a jail run by the extremists, as well as the National Hospital and a small part of northern Raqqa.

"There are still fighters but the area they control is getting smaller," said Mohammed Khedher of Sound and Picture Organization, which tracks atrocities by IS in Iraq and Syria.

Members of the SDF escort a blindfolded civilian detainee suspected to be a member of IS militants. ( Reuters: Issam Abdallah )

Earlier on Friday scores of civilians including women and children fled the last few remaining neighbourhoods held by IS in Raqqa, ahead of an anticipated final push by US-backed fighters seeking to retake the city.

Activist group Raqqa Is Being Slaughtered Silently said on its Facebook dozens of buses had entered the city, "headed from the northern Raqqa countryside towards Raqqa city last night".

The group did not know why the buses were there, but during the more than six-year Syrian conflict, the arrival of buses in a conflict zone has often signalled an evacuation is about to begin.

IS using civilians as human shields, US-led coalition says

A new video that emerged Friday shows desperate, terrified residents emerging from destroyed districts, some of them collapsing on the ground in exhaustion as they arrive.

They seemed to be taking advantage of a slowdown in the fighting and airstrikes by the US-led coalition amid efforts to ensure the safe evacuation of an estimated 4,000 civilians who remain trapped in the city.

Civilians who escaped at Raqqa's frontline rest at a mosque. ( Reuters: Erik De Castro )

The coalition said IS militants are holding some civilians to use as human shields, preventing them from escaping as the fight enters its final stages.

The city on the banks of the Euphrates River has been badly damaged by the fighting, and activists have reported over 1,000 civilians have been killed there since June.

The video released by the Turkey-based Kurdish Mezopotamya Medya showed clearly petrified residents running toward safety, some clutching babies or wounded people.

"This is my husband, we are civilians!" one woman cried, fearing fighters from the US-backed force known as the Syrian Democratic Forces would take him away.

Some of the arriving men were searched before being allowed in while others kissed the ground in relief.

"God is stronger than them [IS]," shouted another woman, clutching what appeared to be a large Koran in her hand.

Another elderly man hobbled out on crutches, begging for water. After drinking from a bottle handed to him, he collapsed on the ground in exhaustion.

Gunfire could be heard in the background.

Smoke rises near the stadium where the IS militants are holed up after an air strike. ( Reuters: Erik De Castro )

AP/ Reuters