BEIJING, Sept. 17 (Xinhua) -- The world's highest power transmission and transformation project started construction Tuesday in the Tibet Autonomous Region.

With a total length of 1,689 km, the project, which goes from Xigaze city to Ali Prefecture, stretches across permafrost, no man's land and swamps.

The project requires a total investment of 7.4 billion yuan (about 1.05 billion U.S. dollars) and is planned to be completed in 2021, benefiting nearly 380,000 people along the line.

With towers at an average elevation of over 4,000 meters, the project is said to be an extremely difficult "power heaven road" due to the harsh construction environment, dangerous road conditions, poor logistics support and strict environmental protection requirements.

The project connecting 10 Tibetan counties will end the days when the power grid of the Ali Prefecture is isolated from the rest of Tibet, thus improving the reliability of power supply in the prefecture, industrial sources said.

It will also help Tibet's poverty reduction and paves the way for the supply of Tibet's clean energy to South Asia, the sources said.

Since 2007, the State Grid Corporation of China has injected 14.5 billion yuan into Tibet's power grid construction, effectively improving the local power supply.