Tonga has formally joined a group of nations calling for a Fossil Fuel Non-Proliferation Treaty.

Prime Minister of Tonga Hu'akavameiliku Siaosi Sovaleni made the official announcement at the Fifth Pacific Regional Energy and Transport Ministers' Meeting in Port Vila on Thursday.

Vanuatu and Tuvalu were the first state parties to endorse the Fossil Fuel Non-Proliferation Treaty.

"Climate change is the single greatest threat to Tonga and Pacific Island countries, and Tonga therefore stands together with our neighbours in calling for urgent action to combat the root cause of this crisis," Hu'akavameiliku said.

In March, Tonga joined a group of Pacific countries - Vanuatu, Tuvalu, Fiji, the Solomon Islands and Niue - making an ambitious call for a global phase out of fossil fuels, and a just transition from fossil fuels in the Pacific, the Port Vila Call.

"Now we urge all Pacific governments to join Tonga, Vanuatu and Tuvalu in publicly calling for the negotiation of a Fossil Fuel Non-Proliferation Treaty," he said.

"A new global treaty can provide the framework for finance, technological support and knowledge sharing needed to ensure a just transition away from coal, oil and gas across the Pacific and in the world."

Environmental organisation 350.org Pacific's managing director Joseph Sikulu said Vanuatu, Tuvalu and Tonga have stepped up to the plate and now it is time for world leaders to decide if they want to be a part of the solution.

"As Pacific Climate Warriors, it fills us with hope to see our leaders continue to show the world true climate leadership," Sikulu said.

Sikulu said this leadership is a commitment to do what is needed to transition Pacific economies away from fossil fuels and keep global warming to below 1.5 degrees.

"In Tonga we say, 'Ko Tonga moʻunga ki he loto' meaning, 'in Tonga our mountains are within, our strength-hold is our heart' and we thank the Tongan government for standing up for our people."