[Read more live coverage of the climate strikes.]

They packed Foley Square and the streets around City Hall, and jammed the stairs leading out of nearby subway stations. They carried handmade signs like one that said, “There is no plan(et) B,” and chanted, “Sea levels are rising and so are we!” Later, they paraded out of the square, headed to another rally at Battery Park.

Frustrated by what they consider officials’ failure to adequately address a crisis, thousands of young people marched through Lower Manhattan on Friday during a day of global climate protests.

Those who rallied said that too little was being done to stem the rise of planet-warming greenhouse gas emissions. One test of their message will come on Monday, when world leaders convene at the United Nations to discuss what they are ready to do about climate change.

The crowd totaled at least 60,000, according to an afternoon estimate from Mayor Bill de Blasio’s office. In a sign of how difficult crowd sizes can be to pin down, organizers put the figure at 250,000. A permit had been issued for 5,000, prompting some organizers to joke that their efforts to publicize the event had been too successful.