The 18-year-old activist, who launched the Fridays for Future movement three years ago, spoke at the opening session of the Youth4Climate talks in Milan on Tuesday.

She was joined by 400 other young climate activists from around 190 countries, and spoke in front of Italy’s minister for ecological transition, Roberto Cingolani, and Milan’s mayor, Beppe Sala.

In a hard-hitting speech, Thunberg demanded climate justice.

“Build back better. Blah, blah, blah. Green economy. Blah blah blah. Net zero by 2050. Blah, blah, blah,” she said.

“This is all we hear from our so-called leaders; words that sound great but so far have not led to action.

“Our hopes and ambitions drown in their empty promises.

“They invite cherry-picked young people to meetings like this to pretend that they listen to us.

“But they clearly don’t listen to us.

“Hope is not blah, blah, blah. Hope is telling the truth. Hope is taking action. And hope always comes from the people.”

Carbon emissions are on track to rise by 16 per cent by 2030, according to the UN, rather than fall by half, which is the cut needed to keep global warming under the internationally agreed limit of 1.5°C.

Thunberg said it is not too late to reverse this trend, but that drastic action would be needed.

“The climate crisis is a symptom of a broader crisis: the social crisis of inequality, which comes from colonialism,” she added.

“A crisis that stems from the idea that some people are worth more than others.”

The Milan talks are set to last for five days and are hosted by the Italian government ahead of the 2021 UN Climate Change Conference, or COP26, a major summit due to be held in Glasgow from October 31 to November 12.

The UN COP26 conference aims to secure more ambitious climate action from the nearly 200 countries who signed the 2015 Paris Agreement.

The proposals being put forward by the youth activists in Milan will be vetted by some 50 climate and energy ministers at a pre-COP26 summit at the same venue on Thursday, and some will make it to Glasgow.

Thunberg will also meet with Italian Prime Minister Mario Draghi on Thursday.

On October 1, Thunberg will attend the Milan rally for Fridays for Future, the global movement that she launched, which involves school students swapping classes for demonstrations to demand action to prevent further global warming and climate change.