Around 1.4 million young people worldwide are expected to ditch school on Friday to march for the environment and urge politicians to take more decisive actions to tackle climate change.
Pupils and students from Australia and New Zealand kicked off the now weekly strikes on Friday, with Japan, South Korea and the Philippines then following on. Marches are scheduled to take place in at least 119 countries.
The "Fridays For Future" movement was launched by Swedish teen activist Greta Thunberg in August last year as a way to call on candidates in her country's general election to commit to reducing carbon emissions.
The 16-year-old has since taken part in rallies around the world and spoken at the United Nations and European Parliament.
In Europe, this week's protests are more politically-charged than usual as voters across the European Union have started casting their ballot for parliamentary elections.
For people too young to take part in the election, the marches are seen as the only way to have their voices heard about the issue and ensure that climate change is put at the core of the next EU Commission's agenda.
They are calling on lawmakers to commit to measures including an end to fossil fuel, zero emission of greenhouse gases and help for workers, industries and developing countries to transition into cleaner economies.