Polish forces have used tear gas and water cannon against migrants trying to cross into the country from Belarus.
Videos showed migrants throwing stones and other objects at the Polish forces guarding a fortified border crossing.
For weeks, thousands of migrants, mostly from the Middle East, have been gathering at the Belarus border in an attempt to reach the European Union.
Belarus has been accused of pushing migrants to the border to try to destabilise the EU, a charge it denies.
EU-Belarus relations have been severely strained since long-term leader Alexander Lukashenko declared victory in a discredited presidential election last year and tried to silence dissent by cracking down on mass protests and arresting political opponents.
The EU imposed sanctions on Belarus in the wake of the poll and, along with the US, will step them up following the border crisis.
There have been more than 5,000 attempts by migrants to cross the border into Poland from Belarus so far this month, compared to just 88 in the whole of last year, the Polish border agency says.
