Thousands of migrants who were stuck at the Greek border have pushed through police lines and entered Macedonia, according to reports.
Macedonian police are reported to have fired stun grenades in response, according to BBC.
A huge number of migrants — most of them fleeing war in Syria — has amassed in recent days, after Macedonia sealed its southern border and declared a state of emergency.
AFP reported some 2,000 refugees spent a rainy night at the border Friday, as police doubled the barbed wire fence in a bid to keep them from crossing. Hundreds more migrants could be seen arriving Saturday morning.
The chaos Saturday started when police decided to allow a group of migrants with small children to cross the border and crowds pushed from the back, squeezing them toward police lines.
Many women, at least one pregnant, and children fell to the ground apparently fainting after making it past the cordon, according to AP.
Then, thousands of others used the moment to run across a field not protected by barbed wire to enter Macedonia. Police fired stun grenades, but didn't manage to stop the rush. Several people were reported injured.
More than 160,000 have arrived in Greece so far this year, though few in any wish to stay. Most want to make it through to more economically prosperous countries like Germany, the Netherlands and Sweden.
Some 45,000 migrants have crossed through Macedonia on their way to northern Europe over the past two months. Saturday marked the second day of clashes between migrants and Macedonian police.