The march has become a point of friction between Poland's hard-right and conservatives on one hand and the liberal centre, in power since a general election last year ended eight years of nationalist rule, on the other.

The government of Donald Tusk has been in power since December but its leftist and centre-right junior coalition members are struggling in opinion polls amid infighting over key campaign issues such as a return of abortion rights.

The far-right Confederation, whose politicians are among the event organisers, appears to have edged up since the election, now polling at around 12%, mirroring gains in parts of Europe in an anti-migration backlash.

"We join this march ... with one intention. We want the patriotic camp to be united, we want the patriotic camp to walk together in this march and in other political undertakings," Jaroslaw Kaczynski, head of the nationalist Law and Justice (PiS) party, told a news conference before joining the event.

"So that Poland is sovereign and its nation is not subject to leftist experiments that damage social structures."

During eight years in power, PiS sought to instill more conservative, traditional family values in public life, including the introduction of a near-total ban an abortion, and to exert control over media and judiciary.

Thousands carried red-and-white Polish flags on Monday, while some chanted "White Europe of brotherly nations!" or "Stop the European Union!", or carried banners reading "Stop mass migration" or "Stop turning Poland into Ukraine".

While both the nationalist PiS party and the Tusk coalition staunchly support Ukraine in its war against Russia, with the backing of the majority of Poles, some are frustrated by the influx of refugees from their eastern neighbour.

Warsaw authorities said some 90,000 people took part in the march, while organisers put the attendance at around 200,000.