A convoy of trucks carrying hundreds of civilians, including men, women and children, left the last enclave held by Islamic State militants in eastern Syria on Wednesday, signaling a possible end to a standoff that has lasted for more than a week.

An Associated Press team in Baghouz, a village near the Iraqi border where the Islamic State group is making its final stand, counted at least 17 trucks that emerged through a humanitarian corridor used in past weeks to evacuate people from the militants' last patch of territory along the Euphrates river.

Women, children and men, some with checkered headscarves, or keffiyehs, could be seen through a flap opening on the flatbed trucks. One man carried a crutch; the women were engulfed in conservative black garments covering their faces known as niqabs.

Mustafa Bali, a spokesperson for the Syrian Democratic Forces, the US-backed militia spearheading the fight against IS in Syria, confirmed the trucks were carrying civilians out of the enclave.

Syrian Democratic Forces fighters watch as an airstrike hits territory still held by Islamic State militants in the desert outside Baghouz on Tuesday. AP

It was not immediately clear if IS militants were also on board the trucks. Around 300 militants are believed to be holed up in the enclave, along with several hundred civilians. On Tuesday, Bali said a military operation aimed at ousting the extremists from the area will begin if they don't surrender, adding that such an operation would take place after separating or evacuating the civilians from the militants.

An SDF commander, Zana Amedi, said most of the militants remaining inside the enclave are seriously wounded or sick.

The Islamic State group has been reduced from its self-proclaimed 'caliphate' that once spread across much of Syria and Iraq at its height in 2014 to a speck of land on the countries' shared border.

The SDF has been encircling the remaining IS-held territory for days, waiting to declare the territorial defeat of the extremist group.

Nearly 20,000 civilians had left the shrinking area in recent weeks before the evacuation halted last week when the militants closed all the roads out of the tiny area.