Polish Prime Minister Mateusz Morawiecki has accused Russian President Vladimir Putin of orchestrating an unprecedented wave of migrants trying to illegally enter Poland from Belarus, saying the "attack" threatens to destabilise the European Union.

The accusation came as thousands of desperate migrants were trapped in freezing weather on the Belarus-Poland border, where the presence of troops from both sides has raised fears of a confrontation.

Western critics have for months said Belarus's strongman leader Alexander Lukashenko is luring migrants from the Middle East to his country and then sending them across the border in retaliation for EU sanctions.

"This is part of the inhuman and really gangster-style approach of the Lukashenko regime," a European Commission spokesman, Peter Stano, told journalists today.

Belarus denies the claims and accuses EU member Poland of violating human rights by refusing to allow the migrants in.

Migrants on the Belarusian-Polish border

"We are not seeking a fight," Mr Lukashenko told the state news agency Belta.

"I am not a madman, I understand perfectly well where it can lead," he added.

"But we will not kneel."

Mr Morawiecki visited guards, troops and police at the border today before turning his sights on Russia, Belarus's main international backer.

"This attack which Lukashenko is conducting has its mastermind in Moscow, the mastermind is President Putin," Mr Morawiecki told the Polish parliament.

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Russian Foreign Minister Sergei Lavrov blamed Western military "adventures" in the Middle East for prompting migrants to flee the region.

He also called for a "unique approach" to be adopted for migrants arriving in the EU.

"Why, when it comes to refugees heading to the European Union from Turkey, did the EU provide funding to keep them on Turkish territory?" he told reporters.

"Why can't the Belarusians be helped in the same way?"

'Hybrid attack'

The crisis came to a head yesterday when hundreds of migrants marched to the border in a bid to cross, but were blocked by rows of Polish police, soldiers and border guards behind barbed wire.

Both Poland and Belarus said that between 3,000 to 4,000 migrants were now in an improvised camp at the border, near the Polish village of Kuznica.

Journalists have been blocked from the area, but videos released by Belarusian and Polish authorities showed the migrants massed along the razor-wire, huddling by fires and in tents as temperatures hovered around freezing.

Migrants on the Belarusian-Polish border

Poland said Belarus was using the migrants as a weapon, insisting it would not open its border.

"Today the stability and security of the entire EU is at stake," Mr Morawiecki said on Twitter.

"This hybrid attack of Lukashenko's regime is aimed at all of us. We will not be intimidated and will defend peace in Europe with our partners from NATO and EU."

Lawmakers in fellow NATO and EU member Lithuania, which also shares a border with Belarus, voted today to impose a state of emergency over fears the migrants trapped on the Polish border might seek alternative routes.

Lithuania has seen a spike in attempted illegal crossings from Belarus in recent days, with 278 migrants denied entry today - just 81 crossed in all of last year.

Effective from midnight, the month-long state of emergency bans journalists and non-residents from a five-kilometre strip along the Belarus border.

EU urges new sanctions

The Belarusian defence ministry said Poland had deployed 10,000 military personnel to the border without giving prior warning to Belarusian authorities, in what it said was a violation of joint security agreements.

Poland's defence ministry tweeted video footage showing what it said appeared to be a "large group of Belarusian officers" nearing the migrant camp.

Poland's Prime Minister Mateusz Morawiecki

The EU called for new sanctions on Belarus on top of those already imposed over Mr Lukashenko's heavy crackdown on the opposition after a disputed election last year.

EU diplomats in Brussels said the bloc was already working on moves to expand the existing sanctions.

The EU said it was also pushing more than a dozen countries, mainly in the Middle East and Africa, to prevent their nationals leaving for Belarus.

Brussels said that European Council president Charles Michel would travel to Warsaw on Wednesday.

European Council president Charles Michel

Some migrants who made it into Poland told AFP last month that they had been trapped in the woods for a week, with Belarus refusing to allow them to return to Minsk and fly home, while Poland would not let them cross to make asylum claims.

The Belarusian border guard service said the migrants in the camp were mostly Kurds, that their physical and mental condition was "extremely poor" and they lacked water, food and the means to wash themselves.

"The situation is aggravated by the large number of pregnant women and infants among the refugees, who must spend the night on the ground in negative temperatures," it said.