AIR strikes have hit a town on Syria's northern border as Turkey launched a military operation against Kurdish fighters.

Turkish President Recep Tayyip Erdogan announced the start of the campaign, which followed an abrupt decision on Sunday by US president Donald Trump that American troops would step aside to allow for the operation.

After Turkey's offensive began, there were signs of panic in the streets of Ras al-Ayn - one of the towns under attack with residential areas close to the borders.

Kurdish forces have warned the operation could create a "humanitarian catastrophe".

Erdogan claimed in a tweet: "Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area.

He said Turkish armed forces and Turkish-backed Syrian fighters known as the Syrian National Army had begun what they called "Operation Peace Spring" against Kurdish fighters to eradicate what Erdogan said was "the threat of terror" against Turkey.

Minutes before Erdogan's announcement, Turkish jets began pounding the town of Ras al Ayn, according to Turkish media and Syrian activists.

Mustafa Bali, a spokesman for the US-backed Kurdish-led Syrian Democratic Forces, said Turkish warplanes were targeting "civilian areas" in northern Syria, causing "a huge panic" in the region.

Turkey has long threatened to attack the Kurdish fighters and has been massing troops for days along its border with Syria.

Trump later said his decision to pull back US troops fulfilled a campaign promise to withdraw from the "endless war" in the Middle East. Republican critics and others said he was sacrificing an ally, the Syrian Kurdish forces.