On the fourth day of the greatest assault on a European state since World War II, tens of thousands of people marched across Europe in protest of Russia's invasion of Ukraine.

More than 100,000 people gathered in central Berlin, waving placards reading "Stop the War," "Putin's Last War," and "We Stand With Ukraine," in addition to Ukrainian and European Union flags.

Thousands of Ukrainian people, mostly of them children and women, were fleeing the Russian invasion into neighboring nations as missiles crashed down on Ukrainian cities.

Thousands of people streamed toward the Brandenburg Gate, near the Russian embassy, disrupting train and subway service in several parts of Berlin.

The United Nations refugee agency said on Sunday that more than 368,000 refugees, mostly women and children, have fled the conflict into neighboring countries, citing figures provided by national authorities.

Around 80,000 protesters gathered in Prague's central square, with the Czech prime minister letting people know that the country was still reeling from the fear of Russian tanks rumbling into the city more than fifty years ago. 

"Of course, I had to come here today," Jindrich Synek, a pensioner, told Reuters. "One must stand up to evil. I've already had a few experiences with it in this square."

Demonstrations took place in Wenceslas Square during the 1989 Velvet Revolution, which brought an end to decades of Soviet-backed communist rule, as well as protests in 1968, when Soviet-led soldiers invaded communist Czechoslovakia to put an end to changes that angered Moscow.

Around 400 participants gathered in central Copenhagen in front of the Ukrainian embassy, many of them lit candles and left flowers to indicate their support for the Ukrainian people.

Thousands of demonstrators carried Ukrainian flags in central Madrid.

They carried placards that read "Peace," "Stop Putin," and "Putin, you should be afraid: my granny is furious."

"We need to demonstrate that people care, which is why we need as many volunteers as possible. Demonstrations won't stop the missiles, but they can indicate that we're all in favor of the truth," Synek added.

London, Rome and Lisbon also witnessed massive protests.

People in Russia flocked to the streets to express their opposition to the war.

On Sunday, police detained over 1,700 individuals at anti-war protests in 46 Russian cities.

This brings the total number of arrests since Russia's invasion of Ukraine began on Feb. 24 to about 5,500, per the independent protest monitoring group OVD-Info.