Mayors from scores of the world's biggest cities gathered in Mexico Wednesday to plot their strategy for fighting climate change in the face of skepticism from US President-elect Donald Trump.

As leaders of busy, polluted cities home to millions of people, they want countries to push on with adopting the so-called Paris Agreement to limit harmful emissions -- an accord that Trump has cast doubt on.

"In the aftermath of this election there's never been a more important time for those city leaders to stay on course -- the whole world is counting on them," said Clover Moore, mayor of Sydney, Australia.

Mayors from members of the C40 Cities Climate Leadership Group were gathering under the chairmanship of Paris Mayor Anne Hidalgo.

Trump has in the past vowed to tear up international climate agreements, though the Republican real-estate magnate said in an interview last week that he has an "open mind" about supporting global accords.

The billionaire had called global warming a "hoax" invented by the Chinese and not scientifically proven.

Hidalgo has vowed to push "for the world's biggest and most influential cities to mobilize to make sure the Paris Agreement is fulfilled."

"Mexico, Paris and other cities will announce new measures to fight against air pollution," she said.

Mayors of major US cities including Chicago, Washington, New Orleans, Austin and Phoenix are due to attend to discuss potential resistance from Trump, who will take office on January 20 after winning the November 8 election.

Hidalgo and other mayors were due to officially launch the three-day meeting on Wednesday evening.

The C40 groups 85 cities including London, New York, Vancouver, Hong Kong and Seoul.