The United Nations’ top court in a landmark advisory opinion says countries could be in violation of international law if they fail to take measures to protect the planet from climate change, and nations harmed by its effects could be entitled to reparations.

The decision from the world's highest court has been welcomed by developing nations at most risk from climate change.

The International Court of Justice called global warming an “urgent and existential threat” at a closely watched case in The Hague.