Leonardo DiCaprio urged wealthy art collectors to bid at an environmental charity auction in New York as if the planet's fate "depends on us" -- and they responded by splashing out $38.8 million.

Monday's "11th Hour" auction at Christie's featured 33 works of mostly contemporary art, much of it created for the event and addressing environmental themes.

The strong result doubled pre-sale estimates, with nine of the works selling for more than $1 million.

Among the main sellers, Mark Grotjahn's "Untitled" went for $6.5 million and Zeng Fanzhi's "The Tiger" fetched $5 million, both of them doubling their estimates in enthusiastic bidding from around the world.

Most of the proceeds went to environmental protection causes championed by the Hollywood actor's Leonardo DiCaprio Foundation.

Even after the sale, the haul shot up when an anonymous collector donated $5 million to match the prices realized for all three tiger paintings featuring in the line-up "in order to protect tigers," Christie's said.

"The gifts of many other generous donors totaled $500,000, generating an overall amount of $38.8 million," the auction house said.

DiCaprio, currently starring in a lavish new production of "The Great Gatsby," describes his foundation as "dedicated to protecting the last wild places on Earth and the critically endangered species that inhabit them."

A 2013 portrait of DiCaprio himself by Elizabeth Peyton sold for $1.05 million, compared to its $400,000-600,000 estimate.

The Hollywood element added even more glitz to the already luxurious atmosphere of a Manhattan Christie's auction room, with actress Salma Hayek joining DiCaprio in the audience.

However, DiCaprio said the world's embattled environment needs far more help.

"Despite the significant efforts of organizations and individuals all over the world, our modern way of life has caused unprecedented devastation to our oceans, our forests and our wildlife," he said, urging buyers to "bid as if the fate of the planet depends on us."

"We are at the 11th hour, we are facing a tipping point of environmental crisis unprecedented in human history," he said.