Around 2,000 migrants, including women and children, in Belarus left their camps on Monday towards the country's western border with Poland.
Along the border just west of the city of Grodno, migrants, who came with a visa from Iraq, left the camps they built in the forested area.
They had been sitting and waiting at the Bruzgi-Kuznitsa border checkpoint.
The Belarusian State Border Committee said new groups had joined the waiting migrants, adding that there were around 2,100 people at the border seeking to enter Poland.
Migrant crisis on border
In October, Belarus suspended an agreement with the EU, obliging the country to take back migrants that crossed its territory and into the EU.
The EU accuses the Belarusian administration of "using irregular migration as a tool" and "trying to destabilize the EU" by sending migrants to the borders of EU countries Poland, Lithuania, and Latvia.
Polish authorities announced that they would not allow the migrants to enter the country and would send those who managed to enter back to Belarus, while Belarus accuses Poland of not providing humane treatment for people seeking to migrate to Europe.
European Commission President Ursula von der Leyen called on EU member states to approve an expanded sanctions regime against Belarusian officials amid the border crisis.
According to the latest EU figures, 7,935 people tried to enter the bloc via the Belarusian-EU border in 2021, up sharply from just 150 last year.
Polish authorities stepped up border protection on Monday and mobilized more than 12,000 troops after a large group of migrants started marching toward the country's frontier with Belarus accompanied by the Belarusian military.