SDF militia predicts ISIL's last fight to end imminently

A ferocious assault continued on ISIL's final enclave on Wednesday as thousands of fighters and their families poured out of the besieged Syrian town of Baghouz.

The US-backed Syrian Democratic Forces (SDF) said the battle was as good as over and Islamic State of Iraq and the Levant (ISIL, ISIS) faced imminent defeat.

Smoke billowed past burning buildings, lit orange by flares and raging fires, as tracer fire pounded the enclave amid the sound of constant shooting and blasts.

Ali Cheir, an SDF commander, said his force and the coalition pummelled the enclave at night to flush out the fighters. "The objective of our advance is to terrorise IS fighters so they surrender, and for the civilians to come out," he said.

The enclave is the last shred of territory held by ISIL soldiers who have been driven from roughly one-third of Iraq and Syria over the past four years.

SDF official Mustafa Bali said on Twitter late on Tuesday the number of ISIL members who had surrendered has risen to 3,000. Three Yazidi women and four children held captive were rescued, added.

"Once our forces confirm that everyone who wants to surrender has done so ... the clashes will resume," Bali said, adding the group's defeat was very near.

Even as the last shred of its "caliphate" crumbled, the armed group put out a new propaganda video - filmed in recent weeks inside Baghouz - insisting on its claim to leadership of all Muslims and calling on its supporters to keep the faith.

"Tomorrow, God willing, we will be in paradise and they will be burning in hell," it showed an ISIL member identified as Abu Abd al-Azeem as saying.

Live footage broadcast by the Kurdish Ronahi TV showed a series of large explosions lighting up the night sky over Baghouz, apparently from an ammunitions dump blowing up.

"The operation is over, or as good as over, but requires a little more time to be completed practically on the ground," SDF spokesman Kino Gabriel told al-Hadath TV.

The SDF has laid siege to Baghouz for weeks but has repeatedly postponed its final assault to allow thousands of civilians, many of them wives and children of ISIL fighters, to leave. It resumed the attack on Sunday.

Dozens have been killed in clashes in recent days. Hundreds of ISIL soldiers are estimated to be holding out in Baghouz, ready to fight to the death.