PARIS: French President Emmanuel Macron issued a stark warning on climate change at a summit in Paris on Tuesday, telling world leaders "we are losing the battle" against global warming.

"We're not moving fast enough, that's the problem," Macron told the One Planet Summit called to boost the 2015 Paris climate accord, which US President Donald Trump has renounced.

"We must all act because we will all be held to account," Macron told the gathering on an island in the River Seine, adding: "We cannot say we did not know."

Dozens of world leaders and hundreds of ministers, company bosses, and environmentalists attended the meeting held two years to the day since 195 nations sealed the Paris Agreement on curbing emissions.

The absence of the US was keenly felt at the talks, which focused on boosting investment in green energy and divesting from fossil fuels.

Speaking ahead of the summit Macron said he was hopeful Trump would reconsider his decision to take the US out of the climate pact.

"I'm not ready to renegotiate but I'm ready to welcome him if he decides to come back," he told US broadcaster CBS, adding: "I'm pretty sure that my friend President Trump will change his mind in the coming months or years."