US President Donald Trump on Tuesday denounced what he called "the prophets of pessimism" who warn the world is on the verge of a major environmental crisis, during his speech to a crowd in Davos that included Swedish environmentalist Greta Tonberg.

"We must reject the eternal Bansheets prophets and their predictions of the end of the world," Trump said hours after he addressed the World Economic Forum Tonberg in Davos, where she indicated that governments had done "nothing" to tackle climate change.