Environmental activists in Portugal collected about 650,000 cigarette butts and stacked them Sunday in a square in central Lisbon, during a movement to raise awareness of this type of pollutant.

"We asked everyone in Portugal to take part in this community project with the aim of drawing attention to plastic pollution, because plastic is hidden in cigarette butts and many don't know it," said Andreas Noe, the 34-year-old German behind the initiative.

"One butt is a good example of how everyone can start taking action, not just on cigarette butts and waste, but also on ocean issues and ultimately the climate crisis," he added.

The NGOs and individuals who accepted Noe's challenge collected enough cigarette butts in one week to fill around 40 plastic beer barrels that were recycled for new use.

Then they dumped its contents on a tarpaulin to create a mound, on which Noe climbed, wearing a respirator mask to protect himself from the toxic elements of the non-biodegradable cigarette butts.

The activist and amateur surfer settled in Portugal six years ago, then gave up his career as a molecular biologist to devote himself to the environmental cause.

Two years ago, he collected about a million cigarette butts in two months.

"We want to end this problem by encouraging people to throw cigarette butts in the trash, in ashtrays, or anywhere but on the ground," said David Figuera, one of the project's participants.