Environmental campaigner Greta Thunberg has spoken to protesters in Bristol ahead of a march through the city, warning "those in power" she will "not be silenced when the world is on fire".

The teenager was welcomed by chants of "Greta, Greta" as she addressed some 15,000 people at the Bristol Youth Strike 4 Climate (BYS4C) event.

She accused politicians and the media of ignoring the climate emergency and "sweeping their mess under the rug".