Thousands of mothers and their families are rallying in central London to demand action on climate change.
The Mothers Rise Up march is being led by eleven 11-year-olds to represent the deadline of 2030 for tackling global warming, set by the United Nations.
The march, which was due to begin near Hyde Park Corner at noon, ending at Parliament Square, is being held in support of youth strikes nationwide.
Similar marches are taking place across the country and internationally,
Rosamund Kissi-Debrah, whose daughter Ella suffered a fatal asthma attack believed to be linked to air pollution, will also address crowds at the rally.
“I’m a mum from Lewisham fighting to get justice for my daughter Ella”, she said.
“Business as usual – toxic pollution in our streets and our schools – is fuelling a crisis that is making our kids sick and it is families in the deprived areas that are paying the heaviest price.
“We need to do everything necessary to clean up our air and create a safer future for all our children.”
A 2018 report said it was likely unlawful levels of pollution, which were detected at a monitoring station one mile from Ella’s home, contributed to her fatal asthma attack.
Former Blue Peter presenter Konnie Huq will also be rallying in London.
Talking ahead of the event, Ms Huq said: “The Greta Thunbergs of the world have been putting the grown-ups to shame so isn’t it time that we did something for our children and their future when it comes to something as big as our environment and our existence.”
Health Secretary Matt Hancock announced on Saturday that he has commissioned Public Health England (PHE) to carry out a review of the impact of dirty air on the nation’s health.
“This review will help us map out how much disease is caused by dirty air and what steps we are taking to prevent this – something which is at the heart of our work to help people live longer, healthier lives through the NHS Long Term Plan.”