"Obviously, one strike isn't going to change everything, but this isn't the last strike", Hirsi said.
Schoolchildren in Cambridge have set up an eco-council to work together to learn about, and find solutions to, the climate and ecological crisis.
At a rally in Stockholm on Friday, Thunberg said the world faces an "existential crisis, the biggest crisis humanity ever has faced and still it has been ignored for decades by those that have known about it".
The demonstration comes after thousands of young people across the United Kingdom took part in a Youth Strike 4 Climate march in February, this time joined by their peers in more than 100 countries around the world from Spain and Germany to Japan, Nepal and Mauritius.
The global strike was inspired by 16-year-old Greta Thunberg, who decided last August she was going to miss school on Fridays and picket outside the Rikstag, otherwise known as the Swedish parliament, to raise awareness about global warming instead.
Classrooms in capitals from Lagos to London are expected to be empty, as the ambitious organisers of the worldwide student strike hoped to stage 1,000 demonstrations in more than 100 countries.
While the protest was to be composed primarily of university and CEGEP students, many high school students are expected to also join in, as well as some teachers.
16-year-old Swedish activist Greta Thunberg nominated for Nobel Peace Prize
Students briefly stopped traffic at a pedestrian crossing chanting "System change, not climate change" and "Climate, change it back", before marching through a shopping centre.
"I had to go down into the city to file the permits and figure out all the sound technology we need", says Xiang. Some students were also planning brief walkouts at their local schools.
"We don't want to strike", the 14-year-old said.
"That's why they need our support", he said. Failure to act, authors cautioned, will result in dire and irreversible consequences for both the environment and the world's population. "I believe more in unicorns than in the will of politicians to save the planet", said another. That, I feel, is very unfair".
His comments came as a report showed Australia's annual carbon emissions had reached record levels, raising questions it will meet targets agreed under the 2015 Paris climate agreement. How can we just go on living our normal lives and doing business as usual when our leaders are doing nothing?
"We are choosing to rise up and take direct action where older generations have failed", they said in an emailed statement (that's right, these kids are so well-organized they're sending out press releases). "It's imperative that leaders and legislators in this Capitol recognize our deep concern for climate change".