Idomeni, Greece (AFP) - Hundreds of refugees on Monday (Feb 29) tried to break through a border fence into Macedonia from Greece where more than 6,000 people are stranded, as Germany lashed out at EU states for abandoning Greece to refugee chaos.

Macedonian police fired tear gas as a group of some 300 Iraqi and Syrian protesters forced their way through a Greek police cordon and raced towards a railway track where they tried to get through the barbed wire marking the frontier between the two countries, an AFP correspondent said.

"Open the borders!" they shouted, prompting police to fire volleys of tear gas which prevented them from crossing.

The angry protest took place several hours after Macedonia allowed some 300 Syrians and Iraqis to cross before resealing the frontier, keeping thousands of others out.

With Austria and Balkan states capping the numbers of migrants entering their territory, there has been a swift buildup along the Greece-Macedonia border with Athens warning that the number of people "trapped" on its soil could reach as many as 70,000 by next month.

As the bottleneck showed little sign of easing, German Chancellor Angel Merkel lashed out at a raft of restrictions imposed by Austria and the Balkan states, saying they risked plunging debt-ridden Greece into refugee chaos.

"We can't just abandon this country," she said in an interview late on Sunday, pointing the finger at Austria, whose introduction of restrictions on February 19 triggered a domino effect.

"When one insists on his border, the other suffers. That's not my Europe."

On the ground, thousands continued to mass at the Idomeni crossing in the hope it would be opened after a day of protests in which scores of people lay down on the railway tracks, among them women and children, some holding slogans reading "Open borders" and "We are humans, not animals".

Macedonia had allowed in another group of 300 on Saturday night, Greek police said.

The build-up at Idomeni camp, which can accomodate up to 1,500 people but is currently sheltering more than 6,000, began in earnest last week after Macedonia began refusing entry to Afghans and imposed stricter controls on Syrians and Iraqis.

EU members Slovenia and Croatia quickly followed suit along with Serbia, with all four states imposing a daily limit of 580 migrants.

The spate of border closures was sparked by Austria's announcement it would accept no more than 80 asylum claims per day and cap the numbers of those seeking to cross its territory, in a move Merkel said was responsible for the current buildup.

"Because Austria decided on a limit of 80 per day, and not one more, we have reached today's situation," she said in a TV interview with public broadcaster ARD late on Sunday, saying the move and the subsequent border restrictions in the Balkans had left Greece in the lurch.

"Do you seriously believe that all the euro states that last year fought all the way to keep Greece in the eurozone - and we were the strictest - can one year later allow Greece to, in a way, plunge into chaos?" she said.

But Austria quickly hit back at criticism of its tougher migrant policy, describing it as "absurd".

"We don't have to take criticism from anyone on any side," Interior Minister Johanna Mikl-Leitner told the Austria Press Agency of the move, which has sparked a bitter standoff with Athens and come under fire from the European Union.

"Apparently for some, the European solution (to the crisis) is for all (migrants) to mass in Austria," she said.

Austria says that its measures and those of Balkan countries, which are only allowing 580 migrants to enter per day, are necessary because efforts towards a common EU policy have failed so far.

Austria, which took in 90,000 asylum-seekers in 2015 and saw almost 10 times as many pass through, last week hosted a migration conference for Balkan countries at which it persuaded them to also impose tougher controls.

Neither Greece nor Germany were invited to the talks, underscoring the deep rifts within the EU as it faces the biggest influx of migrants since 1945.

In Athens, ministers were on Monday to attend an extraordinary meeting to piece together an "emergency" plan to tackle the problem, Greek media said.