UN chief Antonio Guterres has said the world should end the fossil fuel age to curb what he says is a devastating level of melting of glaciers in the Himalayas due to global warming.

The UN secretary-general addressed Nepal’s parliament after flying past Mount Everest, the world’s highest peak, on Monday and touring the base camp of Mount Annapurna, the world’s 10th highest, on Tuesday.

“Glaciers are melting at records. I was a witness,” Guterres said in his address.

“The effect is devastating. Swollen lakes bursting, rivers and seas rising, cultures threatened. And mountainsides exposed, inflaming the risk of rock slides, landslides and avalanche.”

Mr Guterres visited towns including Pokhara where where trekkers begin journeys in the Mount Annapurna region, and met with local groups to discuss environmental issues, including protecting the Himalayan glaciers that provide fresh water to more than a billion people.

“I am here today to cry out from the rooftop of the world: Stop the madness,” Mr Guterres said. “The glaciers are retreating, but we cannot,” he said. “We must end the fossil fuel age.”

A report earlier this year by the Nepal-based International Centre for Integrated Mountain Development said that Himalayan glaciers could lose up to 80% of their glaciers if the earth warms by 4C in coming decades or centuries.

Mr Guterres urged countries to stick to commitments under the 2015 Paris climate conference to control carbon emissions to keep warming down to 1.5C.

“We must act now to protect people on the frontline. And to limit global temperature rise to 1.5 degrees Celsius,” Mr Guterres said.

Scientists warn that flash floods and avalanches could become more likely in coming years, in part due to climate change.

Mr Guterres also appealed to the international community to donate funding to help build resilience in affected communities.