'School students around the world have gone on strike to demand action on climate change.
Organisers expect more than one million young people to join the protests in at least 110 countries on Friday.
They are calling on politicians and businesses to take urgent action to slow global warming.
The strikes are inspired by student Greta Thunberg, who has become a global figurehead since protesting outside Sweden's parliament in 2018.
Carrying a "school strike for climate change" sign, the then 15-year-old said she was refusing to attend classes until Swedish politicians took action.
The solo protest led to various movements across Europe, the US and Australia, known as Fridays for Future or School Strike for Climate.
The last co-ordinated international protest took place on 15 March, with an estimated 1.6 million students from 125 countries walking out of school.
The strike begins
The action on Friday began in Australia and New Zealand.
In Melbourne, 13-year-old Nina Pasqualini said she was joining the strike because she was worried about "weather disasters".
"Every time we have huge a bushfire here another animal might go extinct," she told Reuters news agency.'
Read more: School students walk out in global climate strike