The Polish border guard on Sunday accused security forces on the Belarusian side of preparing stranded migrants there to storm the border fence.
Many tents are said to have been cleared at the camp in Belarus directly opposite Poland's border crossing of Kuznica.
"Foreigners get instructions, equipment and tear gas from Belarusian officials," a tweet from the Polish border guard said.
The Defence Ministry in Warsaw noted that the migrants had gathered branches from the forest and that many Belarusian media representatives were at the site.
Polish police used loudspeakers to warn the crowds in English that violence would be used if they didn't follow instructions.
The reports cannot be independently verified since journalists and aid workers have been denied access to the area ever since Poland declared a state of emergency along its border. Similar restrictions are in place on the Belarusian side.
For several days now, thousands of migrants from third countries have been stranded in makeshift woodland camps at the Polish border as temperatures hover around freezing.
Crowds have also gathered at the Latvian and Lithuanian borders, as the migrants seek a way into EU territory.
Retaliation
Belarusian President Alexander Lukashenko has been accused of orchestrating the crisis at the European Union's eastern frontier in retaliation for sanctions slapped on his regime. He has allegedly allowed people from crisis areas to fly to Minsk so he could divert them to EU countries on his border.
Belarusian opposition-aligned channels on the encrypted messaging app Telegram published videos on Sunday afternoon purporting to show larger groups of migrants approaching the Polish border. "There are more and more migrants," according to the Nexta channel.
Late Saturday, a group of about 50 migrants managed to push through a barrier near the village of Dubicze Cerkiewne. They were in Poland for several hours before being apprehended, according to Polish police.
The group was taken straight back to the Belarus border.
Critics say immediate pushbacks of asylum seekers violate international law.
But due to emergency laws currently in place for the border region, Poland says any person who enters the country illegally must leave. The EU member state has also restricted civil rights and banned demonstrations in the zone.
A separate attempt to break through the border near the town of Kolonia Klukowicze was unsuccessful, Polish authorities said. One officer was injured when the migrants threw stones at the authorities.
No shelter
Many of the immigrants have no shelter, or only rudimentary accommodation set up in the woods.
A 20-year-old Syrian man was the latest victim to be discovered dead at the open-air camp. His body was found on Saturday.
Poland, Lithaunia and Latvia were considering calling a NATO meeting in response to the crisis, Polish Prime Minister Mateusz Morawiecki said on Sunday.
Meanwhile, Latvia began a previously unannounced military exercise over the weekend at its south-eastern border with Belarus. Some 3,000 soldiers from the nation's regular and volunteer armed forces are to take part, Defence Minister Artis Pabriks said on Sunday on television.
The manoeuvre, which will run until December 12, is intended to train large-scale cooperation between various military units and command structures, as well as logistics and mobility, according to a Defence Ministry spokeswoman in Riga.
Member states of the Organization for Security and Co-operation in Europe (OSCE), including Russia and Belarus, have been informed about the exercise, she told the LETA news agency.
Russian President Vladimir Putin, a close ally of Lukashenko, said in a state television interview on Sunday that Moscow was ready to "go to any length" to help find a solution to the crisis.
Many of the migrants are hoping to enter Germany and rumours have been passed circulating that, starting on Monday, there will be buses that would take them to the German border.
The German Foreign Office denied the rumours on Twitter, saying: "Whoever spreads these lies puts people in great danger."
