Pressed against coils of razor wire and shouting “Help us!”, refugees and migrants at Greece’s northern border have been pushed back by Macedonian police using tear gas and stun grenades.

Greek authorities meanwhile are racing to build more camps to shield the escalating number of stranded people from winter.

A top European Union official prepared to visit the region on Tuesday to try and ease the crisis that produced more scenes of chaos: Syrian and Iraqi refugees and others forced their way through part of a Macedonian border fence, some clutching infants or struggling to free duffel bags caught in the razor-wire. They were met by Macedonian riot police.

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Volunteer doctors said at least 22 migrants, including 12 children, were treated for breathing difficulties and cuts.

Authorities in Macedonia said a policeman was injured and that dozens of special forces officers were flown in by helicopter to help quell a refugee protest.

“Tragically, there seems to be more willingness among European countries to co-ordinate blocking borders than to provide refugees and asylum-seekers with protection and basic services,” said Giorgos Kosmopoulos, head of Amnesty International in Greece.

About 7000 migrants, mostly from Syria, Iraq and Afghanistan, are crammed into a tiny camp at the Greek border village of Idomeni, and hundreds more are arriving daily.

Migrants have crammed into a small camp on Greece’s northern border. Photo: EPA

The Greek army completed more temporary shelters in northern Greece over the weekend, and at the government’s request, local authorities in central Greece opened indoor stadiums, conference centres, and hotels that have gone out of business to house migrants, while the education ministry called on schoolchildren to join the effort with donation drives.

“Of course Greece over the next one or two months will do what it can to help these people. But it must be made clear that the burden of this crisis must be distributed in Europe,” Greek Prime Minister Alexis Tsipras said in an interview with private Star television.

The border bottleneck began 10 days ago, when Austria and four ex-Yugoslav countries on the Balkan migrant route north into Western Europe cut border access for migrants to a trickle.

European Council President Donald Tusk begins a tour of those countries on Tuesday, starting in Vienna, which has been strongly criticised by other EU nations for its caps on asylum-seekers, and ending on Thursday in Athens.

Tusk is aiming to prepare for a meeting of leaders from the EU and Turkey on March 7, where the key topic will be trying to halt the flow of migrants from Turkey to Greece.

The number of migrants stranded in Greece topped 25,000 on Sunday, according to government estimates. Thousands have been sleeping outside in parks and fields and even along highways, as refugee shelters quickly overflowed.

So far, border closures have not stopped migrants from coming.