In an emotional speech at the UN Climate Action Summit in New York on Monday, she said they would not forgive the world leaders "if you choose to fail us".

She and 15 other children later filed a complaint against five countries over the climate crisis.

In a passionate speech to world leaders, accusing them of betraying her generation by failing to act on climate change, Thunberg said: "We will not let you get away with this."

"And if you choose to fail us I say we will never forgive you," she said.

"Right here, right now is where we draw the line. The world is waking up. And change is coming, whether you like it or not."

Directly after her speech she, with 15 other children, delivered an official complaint on the climate crisis' impact on youth to the United Nations Committee on the Rights of the Child.

Governments were asked to bring plans not speeches to the UN Climate Summit, in the hope doing so would reset climate geopolitics ahead of a deadline next year for countries to upgrade their climate commitments under the Paris Agreement.

There were no substantial new commitments from Heads of Government, some speeches were empty, however, there were also some examples of the kind of action that, if significantly scaled, could be the answer to the climate emergency.

US President Donald Trump appeared briefly while Chancellor Merkel of Germany and Indian Prime Minister Modi spoke.

Chinese Foreign Minister Wang Yi noted: "The withdrawal of certain parties will not shake collective will of the international community," apparently referring to the US who has flagged its intention to pull out of the Paris Agreement.

Responding to the UN Climate Action Summit, Mohamed Adow, Christian Aid's International Climate Lead, told: "Despite this being called the Climate Action Summit, the concrete outcomes we saw here did not match up with the demands made by science and the schoolchildren who went on strike around the world on Friday."

"The UN Secretary General was right to call it but world leaders clearly failed to live up to the platform he gave them. The few actions that have been announced are far from world changing and that is what is required."

"As Greta Thunberg told them in her opening speech, how dare they."

He added: "It's good to see 59 countries have signalled their intention to enhance their national pledges under the Paris Agreement by 2020. That shows there are some countries that do get the need for action and gives us reason to hope this number, and their overall ambition, will grow over the coming months.