Secretary-General of UN Guterres shakes hands with Swedish environmental activist Thunberg at the UN HQ.

A day after youth-led global climate strikes, several hundred young activists including Greta Thunberg gathered for a climate summit at the United Nations on Saturday, chiding older generations for doing too little to curb carbon emissions.

The UN has invited 500 young activists and entrepreneurs to take part in the New York meeting, the first of its kind, though some were unable to attend after being denied US visas, a point raised by the organizers.

People talk together before the start of the first ever United Nations Youth Climate Summit.

It comes days before a climate action summit which UN chief Antonio Guterres has called to seek greater commitments from world leaders on reducing their greenhouse gas emissions in line with the Paris accord to avert runaway global warming.

The tone for Saturday's event was set by an impassioned speech by Argentine activist Bruno Rodriguez, 19, who led school strikes in his native country.

Kathleen Ma, 23, member of SustainUS speaks during the first United Nations Youth Climate Summit.

"The climate and ecological crisis is the political crisis of our time, it is the economic crisis of our time, and it is the cultural crisis of our time," he said, as Guterres, who was billed as the "keynote listener," watched on.

"Many times, we hear that our generation is going to be the one in charge of dealing with the problems that current leaders have created, and we will not wait passively to become that future: The time is now for us to be leaders."

Jayathma Wickramanayake, UN Secretary-Generals Envoy on Youth (C) wears a t-shirt that says, "There is no planet B."

'Greenwashing' under fire

The corridors of the UN were filled Saturday with young people in formal suits and ties, dresses, and traditional wear from their home countries, and others wearing simple t-shirts and jeans.

But corporations also came under fire for their ties to the oil and gas industries.

The Youth Climate Summit is intended to bring together young activists who are committed to combating climate change.

During one testy exchange, Kathleen Ma, a 23-year-old delegate who lives in New York turned to a representative from Microsoft, which this week announced a deal with Chevron and oilfield services company Schlumberger to provide cloud computing services.

Lucas Joppa, Microsoft's chief environmental officer, thanked her for the question, replying: "That's one that the entire tech sector, and everybody in the world we live in today which is predicated upon an oil and gas economy has to answer. 

Agence France-Presse