Polish forces have used tear gas and water cannon against migrants trying to cross into the country from Belarus.
Some of the migrants at the border threw stones at the Polish forces, the defence ministry says.
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 in an attempt 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.
Poland’s defence ministry said its forces responded to migrants attacking a border fence at Kuznica.
“The migrants attacked our soldiers and officers with stones and are trying to destroy the fence and get to Poland. Our services used tear gas to quell the migrants’ aggression,” the ministry tweeted.
Polish police said Belarusian forces stood by while this happened and accused them of supplying migrants with stun grenades.
A BBC reporter at the scene described his eyes stinging from the use of tear gas, adding that the migrants had been unable to breach the border.
The BBC’s Steve Rosenberg: “A stand-off between the migrants on one side and the Polish police on the other”
The apparent escalation at the border came just as there were signs of de-escalation.
Mr Lukashenko spoke to Germany’s Angela Merkel on the phone on Monday, his first since cracking down on protesters after the election.
He told a government meeting that “we cannot let this so-called problem lead to heated confrontation,” state news agency Belta reported.
The migrants, including children, have been living in makeshift camps in freezing conditions just inside Belarus.