The number of rare tigers in a national park in Nepal has increased by more than one third in the last two years, a study has shown, after authorities set aside more land for the animals.

Experts riding elephants placed cameras in the jungles of the Chitwan National Park in southern Nepal for three months and counted 125 adult tigers, up from 91 two years ago, officials said on Thursday.

"We have sampled more area in Chitwan that is why we have come across more tigers," said Bivash Pandav, tiger coordinator at the Nepal office of the WWF conservation group that helped the count.

Authorities attributed the rise to mainly the expansion of the park area to the neighboring Churia hills hailed as "extremely good habitat" for tiger conservation.

"It is very much possible to double the number of tigers in Nepal and the presence of 125 tigers in Chitwan is an indication to this," Pandav, who coordinates tiger protection activities in 13 countries, said.

These countries include Bangladesh, Bhutan, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Russia, Thailand and Vietnam - all have made a commitment to double the number of tigers by 2022.

Nepali officials said with the latest count in Chitwan the total number of tigers in the Himalayan nation stood at 155.

According to experts barely 3,500 tigers are estimated to be still roaming in the wild in these countries compared with about 100,000 a century ago.

The declining numbers are attributed by experts mainly to poaching and the destruction of their natural habitat by deforestation and encroachment by human beings.