Could Helen Clark be set to be endorsed for UN Secretary-General by one of Hollywood's biggest celebrities?

The former New Zealand Prime Minister and hopeful for the UN top job was photographed sitting next to Leonardo DiCaprio at the United Nations Headquarters in New York on Friday (local time), during the signing of the Paris Agreement.

The agreement to slow climate change was signed by 165 countries, including the world's two top emitters, China and the United States.

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DiCaprio spoke at the signing, praising world leaders for their commitment to addressing an issue he was "absolutely terrified" about.

"Our planet cannot be saved unless we leave fossil fuels in the ground where they belong," he said. "After 21 years of debates and conferences, it is time to declare: no more talk, no more excuses, no more 10-year studies, no more allowing the fossil fuel companies to manipulate and dictate the science and policies that affect our future."

Ms Clark, who currently heads the UN Development Programme has spoken in the past about the importance of tackling climate change because of the devastating impact it will have on the poor.

She has said developed countries have a special responsibility to do more to hit emission reduction targets.

SEE MORE: Helen Clark makes bid for UN top job

Even after signing, the Paris Agreement still needs to be ratified by each country, which in most cases will require a parliamentary vote.

The agreement will only come into force when ratified by at least 55 nations representing 55 percent of greenhouse gas emissions.

Ms Clark faces stiff competition for the Secretary-General role but impressed many during her speech to delegates last week.

Newshub.