While the church leaders who organised the event said it was held for religious reasons, some people felt the national event had anti-Muslim overtones.
The event, "Rosary at the Borders", organised by lay Catholics and endorsed by Polish church authorities, took place in 4,000 makeshift prayer zones and 320 churches, which commemorated the centenary of the apparitions of Fatima, when three shepherd children in Portugal said the Virgin Mary appeared to them.
However, it also commemorated the 1571 naval Battle of Lepanto between Christian fighters, under orders from the Pope, and the Ottoman Empire.
A woman told the BBC: "We come to the border of Poland to pray for the Poles and for the whole world.
"We want our Catholic faith to continue, to keep our children safe, that our brothers from other countries can understand that our faith is unwavering and that we feel safer, not only in Poland but also in the world."
Many elderly braved the cold and criticism to join with their fellow citizens to pray the Rosary. #RozaniecDoGranic 3/ pic.twitter.com/pQDjjpv3uk
— John Frank (@John_Frank1954) October 8, 2017
The Polish broadcaster TVN reported that Poles also prayed in chapels at airports, while Polish soldiers stationed in Afghanistan prayed at Bagram Airfield.
More than 90 per cent of Poland's 38 million citizens are Roman Catholic.
Marek Jedraszewski, the archbishop of Krakow in southern Poland, said during his sermon on Saturday morning that people should pray for "Europe to remain Europe".
He added: "Let's pray for other nations of Europe and the world to understand that we need to return to the Christian roots of European culture if we want Europe to remain Europe."
The day of prayer was endorsed by many Polish celebrities, athletes and several politicians from the ruling conservative Law and Justice party.
However, is also drew criticism online.
Krzysztof Luft, a former member of the country's largest opposition party, the liberal Civic Platform, tweeted: "A ridicule of Christianity on a massive scale. They treat religion as a tool for maintaining backwardness in the Polish backwater."
Poland refused to take part in an EU deal in 2015 to relocate refugees from Italy and Greece.
Pope Francis urged for greater acceptance of migrants on a visit to Poland last year and Bishops have called for the government to assist selected Syrian refugees, albeit without the backing of politicians.
