The last county in China to be accessible by modern land transport was finally linked up to the rest of the country Thursday with a new road that has taken decades to build, state media said.

The 19,000 people of deeply isolated Medog in southeastern Tibet, where the mighty Brahmaputra river -- known as the Yarlung Zangbo in China -- winds its way between towering Himalayan peaks, have until now had to depend on horses for land travel and trade.

The 117-kilometre (73-mile) road took so long to build because of the precipitous topography, China National Radio reported on its website.

Avalanches and landslides also delayed the project, which includes a 3.3-kilometre tunnel that turns a four-hour trek over a snow-capped mountain into a less than four minute drive, it added.

The road is initially expected to be operational for eight months a year, state broadcaster CCTV said.

The area is hit by more than 400 earthquakes annually so alternatives to the road will still be needed to ensure access, the China National Radio report said.

"We will surely have to construct more roads to Medog as it is an earthquake-prone area," it quoted Tu Yunliang, one of the route's designers, as saying.

Critics of Beijing's rule in Tibet say new infrastructure such as railways and airports enable immigration by China's Han ethnic majority, exploitation of its resources and consolidation of political control.

But Beijing insists that such projects raise living standards in the remote region.