Three suicide bombers wearing abayas mingled in with a stream of women, children and wounded men leaving the last ISIS stronghold in eastern Syria and blew themselves up on Friday, killing at least six people.

The attacks targeted surrendering family members of ISIS militants at three crossing points out of the enclave in Baghouz, which is surrounded by the Syrian Democratic Forces (SDF).

As well as those killed, several of those fleeing and in the ranks of the US-backed SDF sustained light wounds. Most of the deaths appear to have been caused by one of the bombers.

"A suicide bomber hid among those fleeing and blew himself up, killing at least six of those who wanted to get out" of Baghouz, SDF spokesman Jiaker Amed said.

It is unclear if the bombers were women or simply wearing women’s clothing although the UK-based Syrian Observatory for Human Rights reported that two women had carried out attacks in the corridor for people to surrender.

Smoke plumes billow from the remains of the last ISIS camps near the village of Baghouz in the eastern Syrian province of Deir Ezzor. AFP

Die-hard ISIS fighters have unleashed a wave of suicide bombings over the past week to impede the SDF advance but the latest incident appears to be the first targeting the group’s supporters leaving the last piece of its self-styled state.

"Daesh has proven to demonstrate a reckless disregard for human life and continues to be a global threat," the US-led international coalition against ISIS said late on Friday, using an Arabic acronym for ISIS.

"We stand by our SDF partners as they fight to liberate that last Daesh-held territory," it said on Twitter.

American aircraft and SDF artillery have been raining shells and rockets down on the ragged remnant of the once sprawling proto-state claimed by ISIS. The bombardment sparked a fresh exodus of ISIS supporters and wounded fighters who joined the dusty march across the front lines to isolated desert reception areas where they are searched and processed.

Before the bombers struck, the SDF said that somewhere in the region of 4,000 ISIS fighters and their families had surrendered en masse.

There were no further surrenders on Saturday, SDF spokesman Adnan Afrin said.

Men who surrender are taken to be questioned before they are incarcerated in SDF jails in north-east Syria while women, children and the elderly are taken to camps several hours from the front lines where they will be held until after the campaign.

Mr Amed said SDF fighters were consolidating their positions around Baghouz as they expected more people to stumble out, although it remains unclear how many are left inside.

Despite dwindling supplies and numbers, hold out hardliners were battling on against the SDF on Saturday. The US has said those still fighting were the most hardened foreign members of the group.

"Clashes broke out again last night and have continued since," Mr Afrin said on Saturday.

During the battle for the enclave, ISIS have hidden in tunnels, deployed suicide attackers against advancing SDF troops and detonated car bombs in a bid to bog down the final battle.

Around 32 militants, including at least four senior ISIS figures, were killed in recent fighting, a statement from the SDF said.

Women walk with their belongings near the village of Baghouz in Deir Ezzor. Reuters

Since the encirclement of the village of Baghouz in the bend of the Euphrates river, tens of thousands of supporters, fighters and some former hostages have abandoned the group. In a matter of weeks, the population of Al Hol displacement camp has swelled from a few thousand to more than 69,000 people.

Among those who fled were a small number of Iraq’s Yazidi minority – many of whom were kidnapped and kept as slaves by the group when it poured over the border and seized several important Iraqi cities. Thousands of other Yazidis were executed by the extremist group in a pogrom described by the United Nations as a genocide.

The SDF has called on international assistance as it says it cannot indefinitely feed, clothe and guard those who have surrendered. Many still hold on to the ideology of the extremist militants and the SDF have confiscated a number of explosives and weapons from those attempting to flee the battlefront. Footage from the SDF reception centres in recent days has shown women chanting ISIS slogans and slurs against the media and the SDF as they board trucks headed for Al Hol.

Inside the camps, a humanitarian emergency is unfolding, with the few agencies on the ground struggling to meet the needs of the ever-increasing number of displaced.

Unicef says Al Hol was designed for just 20,000 people. The International Rescue Committee said that about 122 people, many of them children, have so far died en route to the camp or shortly after arriving, including two on Thursday.

The UN said most of the new arrivals "show clear signs of distress, fatigue, malnutrition and require some form of medical care or attention".