Greta Thunberg has praised climate change activists for their action in Bristol during a speech at a Youth Strike 4 Climate march in the city.

Speaking as the headliner at a demonstration on College Green, the 17-year-old hailed local activists for their successful campaigning against the expansion of Bristol Airport.

She used the recent abandonment of the plans as an example to prove that "activism works".

The 17-year-old also used the opportunity to blame politicians, the media and those in power for not doing enough to help the environment.

She said: "Basically, nothing is being done to halt this crisis despite all thebeautiful words and promises from our elected officials."

WATCH: ITV West Country reporter Robert Murphy meets Greta as she arrives at Bristol Temple Meads station.

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Police said that around 20,000 turned up to see Ms Thunberg, but other estimates suggest the crowd was closer to 30,000.

She told them "nothing is being done" to end the so-called Climate Crisis.

Then she blamed those in power around the world and said: "World leaders are behaving like children, so it falls on us to be the adults."

Reports claim up to 30,000 people gathered to see Greta. Credit: ITV West Country

I will not stand aside and watch. I will not be silent while the world is on fire. Will you?

Greta Thunberg, speaking in Bristol

The 17-year-old is in Bristol today to join a Youth Strike 4 Climate demonstration. She will now march through the city centre with thousands of other young people.

Road closures have been in place since 9am this morning and are expected to be there until 5pm.

On the stage she continued: "We must continue and we have to be patient and remember that the changes required will not happen overnight."

It should not be this way. We should not be the ones who will have to lead on this and tell the uncomfortable truths. Once again, they sweep their mess under the rug for us young people - their children - to clean up for them.

Greta Thunberg, speaking in Bristol
This is what's left of College Green as protesters get ready to march through the city. Credit: ITV West Country

Greta ended her passionate speech by encouraging the crowd to continue campaigning against the impacts of climate change.

The Swedish teenager said: "We will not be silenced, because we are the change and change is coming whether you like it or not."