Kurdish militants in Turkey have issued a new call to arms to defend a border town in northern Syria from advancing Islamic State (IS) fighters, and the Turkish authorities and United Nations prepared for a surge in refugees.

About 70,000 Syrian Kurds have fled into Turkey since Friday as IS militants seized dozens of villages close to the border and advanced on the frontier town of Ayn al-Arab, known as Kobani in Kurdish.

Carol Batchelor, the United Nations refugee agency's (UNHCR) representative in Turkey said the real figure may be more than 100,000 as Turkey faces one of the biggest influxes of refugees from Syria since the war there began more than three years ago.

"I don't think in the last three-and-a-half years we have seen 100,000 cross in two days," she said.

"So this is a bit of a measure of how this situation is unfolding and the very deep fear people have about the circumstances inside Syria, and for that matter Iraq."

A Kurdish commander on the ground said IS militants had advanced to within 15 kilometres of Kobani, whose strategic location has been blocking the radical Sunni Muslim militants from consolidating their gains across northern Syria.

A Kurdish politician from Turkey who visited Kobani on Saturday said locals had told him IS fighters were beheading people as they went from village to village.
Video: Syrian Kurds cross the border into Turkey as Islamic State sweeps over northern Syria. (ABC News)

"Rather than a war this is a genocide operation ... They are going into the villages and cutting the heads of one or two people and showing them to the villagers," Ibrahim Binici, a deputy for Turkey's pro-Kurdish HDP, told Reuters.

"It is truly a shameful situation for humanity," he said, calling for international intervention.
Five of his fellow MPs planned a hunger strike outside UN offices in Geneva to press for action, he said.

The Syrian Observatory for Human Rights, which monitors Syria's civil war, said clashes overnight killed 10 insurgents, bringing the number of IS fighters killed to at least 39. At least 27 Kurdish fighters have died.

IS has seized at least 64 villages around Kobani since Tuesday, using heavy arms and thousands of fighters.

It executed at least 11 civilians on Saturday, including at least two boys, the Observatory said.

"We now urgently need medicines and equipment for operations. We have many casualties," Welat Avar, a doctor in Kobani told Reuters.

"ISIL (IS) killed many people in the villages. They cut off the heads of two people, I saw it with my own eyes," he said, referring to an incident in the village of Chelebi, near Kobani.

The Kurdistan Workers Party (PKK), a rebel group which has spent three decades fighting for autonomy for Turkey's Kurds, renewed a call for the youth of Turkey's mostly Kurdish south-east to rise up and rush to save Kobani.

"Supporting this heroic resistance is not just a debt of honour of the Kurds but all Middle East people. Just giving support is not enough, the criterion must be taking part in the resistance," it said in a statement on its website.

"ISIL fascism must drown in the blood it spills ... The youth of North Kurdistan (south-east Turkey) must flow in waves to Kobani," it said.

Hundreds of security forces cleared the border area south of Suruc of a couple of thousand people who had gathered in solidarity with Kobani for a third day on the Turkish side of the barbed wire fence, where many of the refugees have crossed.