They got the support of aging rocker Mick Jagger and veteran actor Donald Sutherland who were due to walk the red carpet later to present their thriller "The Burnt Orange Heresy".
ADVERTISEMENTAround 300 protesters peacefully took over the red carpet at the Venice Film Festival for several hours on Saturday, demanding action to fight climate change and hoping for celebrity backing.
They sat on the red carpet where Hollywood stars such as Brad Pitt, Scarlett Johansson and Joaquin Phoenix have premiered their latest films during the 11-day festival.
Waving banners that read 'Our home is on fire' and 'No to cruise ships', the protesters sat outside the main festival venue and chanted slogans, surrounded by police.
The protesters, who belong to Italian and foreign groups, were taking part in a five-day Venice Climate Camp event.
They managed to get the support of rocker Mick Jagger and veteran actor Donald Sutherland, who will walk that red carpet later to present their thriller "The Burnt Orange Heresy".
"I am glad they're doing that because they're the ones that are going to inherit the planet," Jagger said at a news conference to promote the movie.
"We're in a very difficult situation at the moment, especially in the U.S. where all the environmental controls that were put in place, that perhaps were just about adequate say for the last 10 years, are being rolled back by the current administration, so much that they will be wiped out."
"I am glad people feel so strongly about it they want to protest anywhere whether it's the red carpet or another place."
Sutherland said environmental protesters had "to fight harder" and "get as much support as they can", adding those calling for the plight of migrants also needed backing.
"When you're my age ... 85 years old and you have children and grandchildren, you will leave them nothing if we do not vote those people out of office in Brazil, in London and in Washington. They are ruining the world," he said.
"We have contributed to the ruination of it but they are ensuring it."