A Philippines island has the world's largest collection of unique mammal species, scientists have discovered, as the area's habitats face danger from hunting and logging.

Twenty-eight new species of cloud rats and earthworm-eating mice have been discovered by US and Filipino scientists in a 15-year study, boosting the number of non-flying mammal species on Luzon to 56, the Chicago Field Museum said in a statement released Friday.

The team, which published the results of its study in the scientific Journal Frontiers of Biogeography last month, said that most of the rare species were found in rain-soaked tropical cloud forests on the island's highland interior.

"The concentration of unique biodiversity in the Philippines is really staggering," said team member Eric Rickart, describing how some individual Luzon mountains hosted up to five species of unique mammals.

The newly documented mammals include four species of tiny tree-mice with long whiskers that nearly touch their ankles, and five mice species that look like shrews and feed mainly on earthworms.

Luzon, about the size of Iceland and the Philippines most populous island, was never connected to a continent, said the Chicago Field Museum mammals curator Lawrence Heaney.

"These animals are isolated high on the scattered mountains, so they inevitably diverge," Heaney added.

But Luzon's 50 million people pose a threat to the species, with over-hunting and habitat destruction.

Ninety-three percent of the country's old-growth tropical forests have already been lost, said Philippines-based team member Danny Balete.

"Protecting all of these species from extinction is going to be a big challenge," he said.