Hundreds of wildlife experts carrying sophisticated cameras began combing the forests in Nepal's southern plains on Tuesday in the Himalayan nation's biggest campaign yet to count the number of endangered tigers roaming in its national parks.

The survey is crucial for planning strategy to double the number of Royal Bengal tigers in Nepal by 2022, as pledged by the Nepali government. Nepal is currently home to 176 of the animals, which are threatened by poaching and habitat loss.

The census will take place in several national parks in southern Nepal - reserves that spread across into neighbouring India, which will be conducting a similar survey on its part of the border.

"Simultaneous counting will help avoid the same tiger which crosses over from one side to the other from being counted twice as its motion will be captured by another camera on the other side," said Maheshwar Dhakal, an ecologist with Nepal's National Parks and Wildlife Conservation Department.

"This way the findings can be very close to accuracy."

Dhakal said technicians would place camera traps along the tigers' paths through the area to capture their images as they move.

Thousands of tigers once roamed the forests in Bangladesh, India and Nepal. But their numbers have plummeted to just about 3,000 now, wildlife experts say.

One big challenge to their survival is illegal trade in tiger parts, which are in high demand for use in traditional Chinese medicine.

In 2010 Nepal committed to double the number of tigers by 2022 by stepping up conservation efforts part of a pledge to international community. The census will become a crucial part of strategic planning towards this goal.

"As part of that commitment we have to increase the number of tigers to 250 in eight years," Dhakal, also the technical coordinator of the tiger count project, said.

"Achieving it looks possible if we can control poaching, protect habitats and involve the local community in conservation."