American children's television network Nickelodeon will not be allowed to build an underwater theme park on one of the nation's most pristine islands, the Philippine environment minister said Wednesday.

Nickelodeon's parent firm announced Monday it would build a "themed attraction" inspired by its cartoon characters such as Dora the Explorer and SpongeBob SquarePants as part of a 400-hectare (1,000-acre) development on Palawan, generating alarm from environmentalists.

Environment Secretary Gina Lopez said Wednesday she would reject the project.

"Lopez says she won't allow the underwater theme park in Palawan. #environment2017," the environment department posted on its Twitter account.

In an interview with ABS-CBN television, Lopez said she would not allow any project that would damage the environment and the welfare of local communities.

"That's our wealth. It's not allowed. You can't kill the corals. For a theme park? No. No way, man," said Lopez, who has been a vocal opponent of mining projects in Palawan.

"The commitment of the government is first and foremost and always, always to the benefit of our people."

Conservation groups call Palawan the nation's "last ecological frontier" because of its relatively untouched coastlines and forests, which are among the oldest and most diverse in Southeast Asia.

Palawan is home to two UNESCO World Heritage-listed sites, a subterranean river and the Tubbataha coral reefs.

Monday's statement by Nickelodeon's parent firm, Viacom International Media Networks, said its resort would open in 2020 and feature restaurants and lounges six metres (20 feet) below sea level.

It also said the Palawan project would "take its place alongside" other Nickelodeon-branded attractions such as Wet'n'Wild in Australia, Teenage Mutant Ninja Turtles Land in Russia and IMG Worlds of Legends theme park in Dubai.

An online petition organised by local environmentalists calling for the project to be stopped attracted more than 125,000 signatures in less than 24 hours.

Viacom's Philippine partner, Coral World Park, issued a statement on Wednesday insisting the development was not a "theme park" and emphasised that it would not all be underwater.

The statement also highlighted the project's "ocean conservation focus" and said it would help fund environmental protection in the area.

It referred to plans for a marine sanctuary and said the Coral World Park would "be the largest coral reef conservation program in Asia".

"There has never been any form of communication from our side mentioning a theme park," said Coral World Park marketing and communications director Susan Lee.

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VIACOM