"There was good forest cover, an ideal habitat and an ideal prey base but tigers were not sighted in the Sahyadri range since the late 1970s," Vishwas Sawarkar, former head of the state-run Wildlife Institute of India, told Reuters.

"My estimate is there are at least 20 of them now," said Sawarkar, adding that the discovery was made during an ongoing nationwide tiger census.

India is believed to have half the world's surviving tigers, but according to a census in 2001 and 2002, their numbers have dwindled to 3,642 from 40,000 a century ago.

Conservationists say the actual number of tigers is between 1,300 and 1,500, based on the initial findings of the current census due to made public later this year.

No sightings of the big cats led many -- including poachers and conservationists -- to believe the tigers had been wiped out from the Sahyadri range, an unbroken chain of mountains that stretch along India's western edge.

Experts said the last remaining tigers could have benefited with poachers moving on to other areas in search of their lucrative prey, whose body parts are used in traditional Chinese medicines and whose skins fetch thousands of dollars.

"Maybe even forest officials and researchers didn't look there properly," Sawarkar said. "This may have helped their numbers grow undisturbed."

Conservationists hope the authorities will now declare Sahyadri a protected tiger reserve.

"Once the tiger reserve is declared, the forest department must be given the necessary means to protect it," said Rahul Kaul, director of conservation at the Wildlife Trust of India.