The International Court of Justice has cleared the way for countries to potentially sue each other over climate change after a judge ruled states must protect people from the "urgent and existential threat" it is having to the environment.

It comes as the United Nations' highest judicial body weighed in on climate change for the first time.

The court had an unanimous opinion that the failure of nations to take action to protect the climate system could constitute "an internationally wrongful act".

However, a judge admitted determining which country caused which part of climate change would be difficult.

The court also found it was a "precondition" for states to protect the environment to ensure human rights.

It added government support for fossil-fuel production could be a potential violation.