Filmmakers from the world over gathered in Berlin for the city's venerable film festival, which is due to be opened later on Thursday with a video address by Ukraine's President Volodymyr Zelenskyy.

Now in its 73rd year, the festival will see 18 films, hailing from Mexico to Australia, competing for a coveted Golden Bear trophy that will be awarded by a jury chaired by U.S. actor Kristen Stewart.

"Full disclosure: I'm kind of shaking," the "Twilight" and "Spencer" star told a news conference to introduce the jury, when asked how she felt about adjudicating at the most overtly political of the world's major film festivals.

Zelenskyy's appearance reflects the organizers' focus this year on Russia's invasion of Ukraine and on pro-democracy protests in Iran. Films from and about both countries are prominent, while films supported by the Iranian and Russian governments are banned.

"This year with Iran, the earthquake, with Ukraine - it feels like the world is disintegrating," said French-Iranian actress Golshifteh Farahani, another jury member.

Outside the main competition, films will tackle topics from race in America to gender transition and sexuality, while high profile visitors will include director Steven Spielberg and singer Bono, attending a documentary about U2's legendary 1997 post-siege concert in Sarajevo.

"If you want to destroy a place the first thing you do is destroy its cinema," said Hong Kong director and jury member Johnnie To, insisting on film's central role in nurturing a democratic society.

"I think it's the job of an artist to take a disgusting and ugly thing and transmute it," Stewart added. "Put it through your body and come up with something more helpful."