Pope Francis on Wednesday urged Europe to find "courageous courses of peace" to end the war in Ukraine as he opened a five-day visit to Portugal for a major Catholic youth festival.

The 86-year-old pontiff has repeatedly called for peace in Ukraine and has sought to play a mediating role, though his efforts have yet to yield results and he has faced criticism for failing to blame Russia for the war.

"We are sailing amid storms on the ocean of history, and we sense the need for courageous courses of peace," he said in an address to officials and diplomats at Lisbon's riverside Belem Cultural Center.

"With deep love for Europe, and in the spirit of dialogue that distinguishes this continent, we might ask her: 'Where are you sailing, if you are not showing the world paths of peace, creative ways for bringing an end to the war in Ukraine'?" Francis received a standing ovation as he arrived in a wheelchair on the stage to deliver his speech, which was peppered to references to Portuguese literature and music.

He arrived in Lisbon to take part in World Youth Day, which is actually a week of religious, cultural and festive events held about every three years in a different city.

Organizers expect a million people from over 200 countries to take part.

Francis, the first Latin American pope, said he hoped this year's event would serve as an "impulse towards universal openness" for Europe.

"For the world needs Europe, the true Europe. It needs Europe's role as a bridge and peacemaker in its eastern part, in the Mediterranean, in Africa and in the Middle East," he said.

The pope, who has made protection of the environment a cornerstone of his pontificate, also warned about the increased warming and pollution of oceans and the subsequent climate risks.

"We are transforming great reserves of life into dumping grounds of plastic," he said. "How can we claim to believe in young people, if we do not give them healthy spaces in which to build the future?"