The study also said more than 11 million people worldwide rely on World Heritage sites for food, water, shelter and medicine, and damaging development could harm them.
Ninety per cent of sites provide jobs and benefits that stretch beyond their borders, and the protected areas help relieve poverty and food insecurity, tackle climate change and promote sustainable use of natural resources, it claims.
WWF is calling on governments to ensure no harmful industrial activities are permitted in World Heritage sites or areas that could affect them, and for businesses to commit to avoid damaging projects.
The Great Barrier Reef is at risk from coal mining activities, the Grand Canyon is threatened by unsustainable water use and the Sichuan Giant Panda Sanctuaries is at risk from oil and gas concessions, the report said.
In Europe, the handful of threatened sites include Donana National Park in Spain, home to millions of birds including flamingos, and the endangered Iberian lynx, where there are plans to reopen a mine that caused environmental disaster in the 1990s.
The report also focuses on the Belize Barrier Reef Reserve System, home to 1,400 species of wildlife, which it says is threatened by coastal construction, large-scale mangrove clearance, harmful run-off from farming and potential oil exploration.
Around half of Belize's population, around 190,000 people, are supported by incomes from tourism and fisheries around the reef, and the damaging activities have led to the protected area being listed as World Heritage in danger, the report said.
David Nussbaum, chief executive of WWF-UK, said World Heritage sites cover about 0.5 per cent of the Earth's surface and include some of the most valuable and unique places on the planet.
"Yet even this small fraction of our planet isn't receiving the protection it deserves," he said.
"These areas contribute to our economies through tourism and natural resources, providing livelihoods for millions of people, while also supporting some of the planet's most valuable ecosystems, so we need to work together now to ensure they are properly protected."
He said nations need to turn away from harmful industrial activities and focus on sustainable alternatives that enhance World Heritage sites, their values and the benefits they provide, especially to local communities.
- AAP