"This is another discovery that clearly shows this is a magical place where you keep finding new species," spokesman Olivier van Bogaert said by telephone from Switzerland.

"This can help to ensure the area is not deforested or converted for short-term economic development."

Chris Dickinson, WWF's chief technical adviser in the area known as the "Green Corridor" in Thua Thien Hue province, said that several large mammal species were found in the same forests in the 1990s. These include the saola, a type of wild cattle that was found by scientists in 1992.

The new butterfly species are among eight discovered in the province since 1996, the conservationist group said in a statement.

It said the new snake species that can reach 80 cm (31.50 inches) long is called the white-lipped keelback and has a yellow-white stripe along its head and red dots cover its body.

Three of the orchid species are leafless, which is rare.

"All these species are at risk from illegal logging, hunting unsustainable extraction of natural resources and conflicting development interests," the group's statement said.