IDOMENI, Greece -- Macedonian police fired tear gas and stun grenades Monday as several hundred Iraqi and Syrian refugees, frustrated at days of delays in crossing the Greek-Macedonian border, broke down a gate at a nearby rail crossing.

Thousands of people have been stuck at Greece's northern border, overflowing from a packed refugee camp at Idomeni into the surrounding fields as they wait for Macedonian authorities to let them continue their trek through the Balkans. Only a tiny trickle of people from specific countries have been allowed to cross every day.

The migrants had earlier pushed their way past Greek police to reach the gate, chanting "Open the border!" and "We want to go to Serbia!" the next country north on the Balkan migration route leading into Western Europe.

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Police repelled the protesters and no arrests or injuries were reported in Monday's clashes.

About 6,500 Syrian and Iraqi refugees are camped at or near the Idomeni crossing, with another 500 moved to a hastily erected camp on a small concrete landing strip 13 miles away.

Macedonia has said it will only allow in as many people as Serbia accepts. This has led to a huge bottleneck in Greece, where authorities say more than 22,000 people are stuck and more are arriving every day.

Macedonian police opened the crossing to receive about 50 people just before midday Monday but closed it again after the clashes. A police spokeswoman said a train with 450 refugees left the Greek border early Monday and was heading for Serbia.

Syrian refugee Nidal Jojack, 45, said she has been camped out with her family at Idomeni for three days and nights.

"Very many people were forced to sleep in the open, without tents, wrapped in blankets," she said. "It was very cold. The borders are effectively closed, it's a huge problem. To get food, we have to wait in very long queues."

Jojack hopes to reach Germany, where her 18-year-old son has already arrived.

The Idomeni crossing is a key point on the mass migration route that has prompted a major Europe-wide crisis. More than a million people have entered the continent since January 2015 - mostly arriving in small smugglers' boats from Turkey on Greece's eastern Aegean Sea islands.

After first sending welcoming messages, European authorities are now struggling to handle the situation. Hungary has fenced off its borders, refusing to accept any migrants, and other eastern European countries say they will not take in anyone under an EU refugee-sharing deal.

In recent weeks Austria -- at the north end of the Balkan corridor -- has severely restricted the inflow of migrants, causing a domino effect through the Balkans. Many countries are now refusing to let Afghan refugees in, although U.N. authorities say no one has explained to them who made this decision or why.

Diplomatic tensions are rising too, with criticism mounting against Austria, while Athens has threatened to block decisions at an upcoming EU-Turkey summit unless the bloc forces members to shoulder a proportionate share of the refugee burden.

Meanwhile, at another major choking-point in the refugee crisis, French authorities began dismantling the sprawling refugee camp in Calais on Monday, taking down tarpaulin roofs and plywood walls that have been the temporary home for thousands of migrants hoping to make their way to a better life in Britain.

A flashpoint on the edge of the Channel, the camp sprang up years ago in the port city, which has both ferries and the Eurotunnel rail to Britain. But it has grown explosively in the past year amid Europe's migrant crisis, now housing about 4,000 people and fueling far-right sentiment in both Britain and France.

One by one, helmeted workers pulled down makeshift structures where migrants sleep in the southern sector of the camp, after a court ruled that the shanties could be destroyed but not the common spaces that have also sprung up, like places of worship, schools and a library.

A cordon of police formed a perimeter around the demolition crews, to block what local authorities described as "intimidation" tactics by activists. French authorities have offered to relocate uprooted migrants into heated containers installed last month nearby or at centers around France where they can apply for asylum.

Many have resisted the move, fearing it will hurt their chances of reaching Britain, and some migrant advocates say there isn't enough space in the new area.

Also on Monday, German Chancellor Angela Merkel issued a robust defense of her quest for a European solution to the migrant crisis. Merkel is resisting calls at home and elsewhere in Europe for limits on refugees like Austria has introduced.

"We can't do this in such a way that we simply abandon Greece," she said Sunday night on ARD television. "This is exactly what I fear: when one country defines its limit, another must suffer. That is not my Europe."

At next Monday's summit, EU leaders "will discuss how we can restore the (passport-free) Schengen system step by step with Greece," Merkel said.

Authorities say over 1,800 people a day have reached Greece's islands from Turkey in February, slightly down from 2,175 a day in January before the border restrictions started to kick in in earnest.

Accidents are frequent as dozens cram into unseaworthy boats provided for a high price by smuggling gangs. Ninety-six people have drowned in Greek waters alone so far this year, with another 34 missing at sea. More than 400 people died or were lost at sea last year in Greek waters.

After long delays, Greek authorities have constructed a series of screening centers and transit camps for migrants. But the centers are now all overflowing, forcing hundreds of families to sleep outside in a central Athens square or at a passenger terminal in the capital's port of Piraeus.