The future of the planet is at stake during hearings at the top United Nations court, a representative for Vanuatu said on Monday, opening a historic case that aims to set a legal framework on how countries should tackle climate change.

More than 100 countries and organisations are set to present before the International Court of Justice (ICJ) over the next two weeks, the highest number ever.

"The outcome of these proceedings will reverberate across generations, determining the fate of nations like mine and the future of our planet," said Vanuatu's representative for climate change, Ralph Regenvanu.

"This may well be the most consequential case in the history of humanity," Regenvanu told the 15-judge bench in the panelled hall of the Peace Palace in The Hague.

Activists hope the ICJ opinion will have far-reaching legal consequences in the fight against climate change, impacting ongoing court cases as well as domestic and international legislation.

Others fear the UN-backed request for a non-binding advisory opinion will have limited impact - and it could take the UN's highest court months, or even years, to deliver.

A handful of protesters gathered outside the Peace Palace, near a big screen reading "We are watching".

Demonstrators had hung banners saying: "Biggest problem to the highest court" and "Fund our future, climate finance now."

The presentations at the scenic Peace Palace come days after a bitterly negotiated climate deal at the COP29 summit in Azerbaijan.

Wealthy polluting countries ultimately agreed to find at least US$300 billion a year by 2035 to help poorer nations transition to cleaner energy sources and prepare for increasing climate impacts such as extreme weather.

Developing countries condemned the pledge as too little, too late, and the summit's final deal failed to include a global pledge to move away from burning planet-heating fossil fuels. (AFP)