Pope Francis on Saturday warned against populism, saying it could lead to the election of "saviours" like Adolf Hitler.

In an hour-long interview with Spanish newspaper El Pais, conducted as Donald Trump was being sworn in as US president, the pontiff also condemned the idea of using walls and barbed wire to keep out foreigners, among them refugees and migrants.

"Of course, crises provoke fears and worries," he said, but added that for him "the example of populism in the European sense of the word is Germany in 1933".

The pope added: "Germany ... was looking for a leader, someone who would give her back her identity and there was a little man named Adolf Hitler who said 'I can do it'."

"Hitler did not steal power," the pope said. "He was elected by his people and then he destroyed his people."

The Germans at that time also wanted to protect themselves with "walls and barbed wire so that others cannot take away their identity", he said.

"The case of Germany is classic," he said, adding that Hitler gave them a "deformed identity and we know what it produced".

Pope Francis, however, underlined that it was too early to pass judgment on Trump.

"Let's see. Let's see what he does and then we will evaluate," he said.

In February, the pontiff, in another apparent warning to Trump, said: "A person who thinks only about building walls - wherever they may be - and not building bridges, is not Christian ... I'd just say that this man is not Christian, if he said it this way."

Populist surge

Populist parties are on the rise across Europe.

Unemployment and austerity, the arrival of record numbers of refugees and migrants in France, Belgium and Germany have left voters disillusioned with conventional parties and led to a rise of Islamophobic sentiment and anti-refugee views.

In Germany, far-right leaders met at a conference amid protests a day earlier.

French far-right leader, Marine Le Pen, told several hundred supporters in the German city of Koblenz that Britain's vote last year to leave the European Union would create a "domino effect".

A day after Trump took office in the US, Le Pen said his inauguration speech included "accents in common" with the message of reclaiming national sovereignty by the far-right leaders.

"2016 was the year the Anglo-Saxon world woke up. I am sure 2017 will be the year the people of continental Europe wake up," she said to loud applause.

Le Pen - head of the anti-European Union, anti-immigrant National Front and seen by pollsters as highly likely to make a two-person runoff vote for the French presidency in May - has marked out Europe as a major plank in her programme.

More than 3,000 demonstrators gathered to protest against the Koblenz conference, while some staged a sit-in outside the hall.

Also in attendance was Dutch hardliner Geert Wilders, who used the platform to repeat Islamophobic rhetoric, the central theme of policies that have pushed his Party for Freedom to the front in the polls in the run-up to elections in March.

The leaders of Europe's established parties were "promoting our Islamisation", Wilders said in a speech.

European women were now "frightened of showing their blonde hair", the Dutch politician said, addressing the enthusiastic audience in German.