Teenage activist Greta Thunberg on Friday said activists' calls on the corporate and political elite at Davos to seriously fight climate change had been "completely ignored", but vowed not to be subdued by stinging personal criticism from the Trump administration.

The 50th edition of the annual Swiss Alps forum wrapped up with the menace of climate change -- which UN Secretary General Antonio Guterres warned could leave humanity "doomed" -- hammered into the minds of participants but doubt over whether any concrete action would be forthcoming.

"Before we came here we had a few demands for this WEF. Of course these demands have been completely ignored. We expected nothing less," Thunberg told reporters in the ski resort on the last day of the conference.

"As long as the science is being ignored -- as the facts are not being taken into account -- and as long as the situation is not being treated as a crisis, then world and business leaders can, of course, continue to ignore the situation.

"They do not have to do anything as they are not being held accountable," she lamented before joining other young people in one of her regular "Fridays for Future" protests in Davos.

IMAGESTeenage climate activist Greta Thunberg takes part in a "school strike" demonstration in Davos, on the last day of the World Economic Forum where she said calls to the corporate elite meeting to immediately disinvest in fossil fuels have been ignore IMAGESTeenage climate activist Greta Thunberg takes part in a "school strike" demonstration in Davos, on the last day of the World Economic Forum where she said calls to the corporate elite meeting to immediately disinvest in fossil fuels have been ignored. Photo: AFPTV / Eloi ROUYER

The Swede had emerged as one of the key figures of the Davos forum, warning "our house is still on fire" and prompting US President Donald Trump to grumble on his visit to the event about the "perennial prophets of doom".

Thunberg says protesters' demands have been completely ignored at Davos Thunberg says protesters' demands have been completely ignored at Davos Photo: AFP / Fabrice COFFRINI

Her demand for an immediate halt to investment in fossil fuels also prompted a stingingly personal aside from US Treasury Secretary Steven Mnuchin on Thursday.

"Is she the chief economist? Who is she? I'm confused," Mnuchin said, emphasising after a pause that this was a joke.

"After she goes and studies economics in college, she can come back and explain that to us," he said.

Asked about Mnuchin's comments, the Swede said: "Of course it has no effect. We are being criticised like that all the time."

Thunberg, 17, emerged as one of the key figures of the Davos World Economic Forum this year Thunberg, 17, emerged as one of the key figures of the Davos World Economic Forum this year Photo: AFP / FABRICE COFFRINI

"If we cared about that, we would not be able to do what we do. We put ourselves in the spotlight."

Mnuchin on Friday launched a new defence of US policy, insisting the Trump administration cared for the environment, but that problems should not be reduced to just climate change.

"Climate change is one of many issues" affecting the environment, he said, adding Trump was a firm advocate of "clean air and clean water."

He said the reason the US left the Paris climate agreement -- which calls for blocking global warming at well below 2C, and 1.5C if possible -- "was not because we don't support the environment (but because) we thought it wasn't a fair and balanced agreement."

He added that there were other key global issues to worry about, notably that "there's way too many people in the developing world" without access to electricity and preventing the spread of epidemics in the next decades like the coronavirus.

The starkest warnings at the forum came from Britain's Prince Charles -- who asked "what good is all the extra wealth in the world... if you can do nothing with it, except watch it burn?" -- and Guterres.

The UN chief warned that the world was losing the war against climate change and humanity's capacity "to live in this planet" will risk being destroyed.

"We need to act in order to make sure we are not doomed," he said.

Another prominent climate change protest leader, German student Luisa Neubauer, acknowledged that some bold words had been heard at Davos, but deeds were now needed.

"From the first day onward, we striked for actual climate action."