A forest fire was raging Wednesday atop a Philippine mountain, threatening endangered plants and animals in an area also considered by some local sects as a holy place, officials said.

The government's National Disaster Risk Reduction and Management Council said about a 10-hectare (24.7-acre) patch of forest near the summit had been destroyed as of early Thursday.

In an advisory it also warned the fire near the summit of Mount Banahaw was still spreading.

Firefighters have still not reached the blaze some 18 hours after it was first observed, said municipal disaster official Elmer Bustamante.

"The area is too steep," he told AFP by telephone from the town of Sariaya at the base of the mountain, about 95 kilometres (59 miles) south of Manila.

Environment officials in the region are surveying the fire aboard military aircraft to check the extent of the damage and see how best to put it under control, Bustamante added.

The cause of the fire is unknown, he said.

Backpackers have been banned from the 2,158-metre (-foot) peak since 2004 to protect its biodiversity.

Several small sects that worship at caves and springs on its lower slopes continue to have access there, though officials said there have been no reports of anyone being trapped in the fire.

Wildlife officials of the environment department told AFP Banahaw's forests, including a 10,900-hectare protected zone, are home to scores of animal species found only in the Philippines, including a species of cloud rat discovered only in 2004.

However, they said they have yet to receive a report of the extent of the damage.

Ivan Herzano, project officer of the non-government group Foundation for the Philippine Environment, told AFP that despite access restictions, forest rangers lacked the capability to track all persons who may be illegally entering the protected area.

"Most likely it was a man-made fire," he told AFP.

Hunters illegally looking for game could have lit dry litter on the forest floor by carelessly discarding cigarette butts, he added.

The foundation has recently completed a 60-hectare reforestation project on the mountain, which has protected zones that are off limits to human habitation as well as "multiple-use zones" on its lower slopes reserved for locals, Herzano added.