"Change is coming," Swedish activist Greta Thunberg said Friday as hundreds of thousands of people hit streets worldwide to take part in another round of climate strikes.

Carrying placards with messages like "Time's running out" and "There's no planet B," young people and their allies across the globe urged world leaders to take swift action to tackle the climate crisis.

Friday's actions kicked off in New Zealand, where organizers said roughly 170,000 people—which represents about 3.5 percent of the country's total population—took part across the island nation.

Auckland-based public health physician Rhys Jones wrote Friday of the turnout, "If our leaders were looking for a mandate to act, this is it."

Friday's strikes cap a week of youth-led climate actions, which began with a bang when over four million people turned out for the global #ClimateStrike on the Sept. 20. The Friday wave of actions, said author and 350.org co-founder Bill McKibben in a tweet, appears to be "just as marvelously massive."

"I think today our message is going to be partly about the fact that you're allowed to be outraged, you should be outraged, and it's only that that's going to save us," Alienor Rougeot from the Toronto chapter of Fridays for Future said Friday.

School strike for climate catalyst Thunberg, for her part, is in Montreal where she plans to take part in that city's climate march.

See images of other strikes below: