Some 66,000 refugees - mainly Syrian Kurds - have crossed into Turkey in 24 hours, officials say, as Islamic State militants advance in northern Syria.

Turkey opened its border on Friday to Syrians fleeing the Kurdish town of Kobane in fear of an IS attack.

Activists say some 300 Kurdish fighters have crossed into Syria from Turkey to help defend the strategic town.

IS controls large areas of Syria and Iraq and has seized dozens of villages around Kobane, also called Ayn al-Arab.

Turkey - which shares a border with Iraq and Syria - has taken in more than 847,000 refugees since the uprising against Syrian President Bashar al-Assad began three years ago.

But the opening of the border has seen a dramatic increase in the past 24 hours.

"As of today, the number of Syrian Kurds who entered Turkey has exceeded 60,000," Turkish Deputy Prime Minister Numan Kurtulmus told reporters on Saturday.

He was speaking from the southern Turkish province of Sanliurfa, where many of the refugees have sought shelter.

Separately, a Turkish government official told the BBC's Mark Lowen that the number is as high as 66,000.

The UK-based Syrian Observatory for Human Rights said at least 300 Kurdish fighters had joined Syrian Kurdish ranks in the Kobane area to fend off the IS advance. The activist group did not specify which Kurdish group the fighters belonged to.

"Islamic State sees Kobane like a lump in the body: they think it is in their way," the observatory's Rami Abdulrahman said.

Syrian activists say IS has seized as many as 60 villages surrounding Kobane since fighting began earlier this week.

The observatory said on Saturday that at least 11 Kurds had been executed by IS, with the fate of some 800 residents who fled the villages "unknown".

The head of Syria's Kurdish Democratic Union, Mohammed Saleh Muslim, has appealed for international assistance in the battle against the jihadists.

"Kobane is facing the fiercest and most barbaric attack in its history," Reuters news agency quoted him as saying.

"Kobane calls on all those who defend humane and democratic values... to stand by Kobane and support it immediately. The coming hours are decisive," he added.

BBC correspondents say the capture of the town would give IS control of a large strip of Syria's northern border with Turkey.

(BBC)