India is planning a new tiger sanctuary inside the world's largest mangrove forest after a previously undiscovered group of the endangered beasts was discovered, wildlife officials say.

The reserve is planned inside the Sundarbans, a forest which straddles the border of India's West Bengal state with Bangladesh, to protect the tigers from poachers and try to boost their numbers.

"The Indian government has agreed in principle to set up a new sanctuary to protect the tigers in the mangroves," Pradip Vyas, director of the government's Biosphere Sundarbans Project, told AFP this week.

India is home to most of the world's tigers and the Sundarbans, an UNESCO World Heritage Site spanning a total of 10,000 square kilometres (3,860 square miles), already has a tiger reserve.

But a survey this year of the forest using hidden cameras found some 22 tigers outside that reserve, prompting government moves to set up the new and smaller sanctuary, Vyas said.

He said the 22 could indicate a boost in overall tiger numbers in India, which was home to 1,706 tigers nationwide according to the last census in 2011.

"We have found the presence of 102 tigers, of which 80 were in the tiger reserve project near Sajnekhali and 22 in the forest on the western bank of the river Malta, site of the new sanctuary," Vyas said.

"What is more encouraging is that six cubs were photographed, besides the grown-up tigers, during the six-month-long census," he added.

The WWF welcomed plans for the new sanctuary, which would cover 538 square kilometres, but called for tougher measures including better infrastructure to stop poachers entering the reserve.

"A tiger shot by suspected poachers was found floating in a tidal river and another big cat, hacked to death, was spotted by villagers in a gunny bag near a ferry ghat (landing place) in the forest," Anurag Danda, director of the WWF-India Sundarbans Landscape, told AFP.

He said more vigilance was needed to curb rising poaching.

The head of the current tiger reserve said security has been stepped up after recent cases of illegal hunting and the new reserve will have "a ring of security guards" to stop poaching.

"Over 20 poachers, arrested recently, are facing trial," said Soumitra Dasgupta, director of the Sundarbans Tiger Reserve.

India's overall tiger population still remains a long way off the estimated 3,700 in 2002.

Authorities across Asia are waging a major battle against poachers, who often sell body parts to the lucrative traditional Chinese medicine market, and other man-made problems such as development leading to habitat loss.