More than 900 Polish troops are involved in the operation, which comes after EU members accused Minsk of opening the gates.
Poland has deployed hundreds of troops to support its border guards at the frontier with Belarus as a surge of refugees and migrants sought to enter the country.
Defence Minister Mariusz Blaszczak said on Wednesday that more than 900 Polish troops were involved in the operation.
It is understood that most of the refugees and migrants trying to cross are from Iraq.
Late on Tuesday, a Polish deputy interior minister tweeted that the border with Belarus is sealed and that the soldiers have been there for a week.
Poland, like Lithuania and other Baltic nations, accuses the authoritarian government of Belarusian President Alexander Lukashenko of sending people across their borders.
They believe Minsk’s moves are retaliatory.
The European Union imposed sanctions on Belarus following a disputed presidential election last year – which the West saw as rigged, as well as for harsh repressions on Belarusian protesters.
On Wednesday, EU ministers also held emergency talks “to determine concrete measures and forms of assistance to the affected states in managing and containing illegal crossings at the border with Belarus, also from the aspect of security at this section of the external EU border,” the Slovenian EU presidency said.
More than 4,100 refugees and migrants have arrived in Lithuania so far this year and are being sheltered in temporary camps across the country.
Lithuania’s border guard service released video footage on Wednesday which it said reveals that migrants are being pushed across the border into EU territory by Belarus riot police.
After talks with Lithuanian Prime Minister Ingrida Simonyte on Wednesday, EU Parliament President David Sassoli accused Lukashenko, once dubbed Europe’s last dictator, of “exploiting these poor people, men and women.”
“I have seen these outrageous actions when officials push people across the border. It is both an issue of human rights, and also a question of protecting the border of the EU,” Sassoli said. “It is an organised activity of the Lukashenko regime.”
On the eve of the meeting, German Chancellor Angela Merkel and Estonian Prime Minister Kaja Kallas accused Lukashenko of launching a “hybrid attack” against the 27-nation bloc by channelling migrants to Lithuania, Latvia, Estonia and Poland in retaliation over the EU’s sanctions.
“We agree that this is hybrid aggression that uses human beings,” Merkel said after their talks in Berlin.
Kallas said that “this is no refugee crisis, but this is a hybrid attack on the European Union.”
Merkel said she would raise the issue with Russian President Vladimir Putin in Moscow on Friday.