Tear gas fired as migrants seek to enter Macedonia from Greece
Police have fired tear gas and stun grenades after a few hundred migrants angry at long delays in entering Macedonia broke a gate on the border with Greece.
The protesters, who were chanting "Open the border" and throwing stones at Macedonian police, were repelled.
There were no reports of arrests or injuries from the latest clashes.
Police said 500 people earlier pushed their way past Greek police to reach the gate, which is used to let trains through at the border crossing.
About 6,500 people are stuck on the Greek side of the border.
Some have been there for up to eight days with little food or shelter as Macedonia only accepts a small number of people every day.
Macedonian police opened the crossing to receive about 50 people just before midday, after keeping it closed for eight hours, but shut it again after the clashes.
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 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 UN authorities say no one has explained to them who made this decision or why.
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 hundreds more are arriving every day.
At Idomeni, 45-year-old Syrian refugee Nidal Jojack said she has been camped out with her family for three days and nights.
She said: "Very many people were forced to sleep in the open, without tents, wrapped in blankets. It was very cold. The borders are effectively closed, it's a huge problem."
Meanwhile, Austria's deputy chancellor rejected criticism from other EU nations over his country's introduction of caps on asylum seekers.
Reinhold Mitterlehner said the "upper limits are necessary (and) we're going to maintain them".
He was referring to the decision to accept no more than 80 requests for asylum a day at Austria's southern border with Slovenia from arriving migrants.
Mr Mitterlehner said Austria continues to seek a solution to the migrant crisis that involves all 28 EU nations. But he told the Austria Press Agency that until that happens "we have to ... create limits".