Tibet on Friday blocked a tributary of the Yarlung Zangbo River as part of its most expensive hydro project.

The Lalho project on the Xiabuqu River in Xigaze, involves an investment of 4.95 billion yuan (740 million U.S. dollars), said Zhang Yunbao, head of the project's administration bureau.

The project was scheduled to be completed in 2019. Construction began in June 2014.

The project serves multiple purposes, including irrigation, flood control and power generation, said Zhang.

Its reservoir was designed to store up to 295 million cubic meters of water and help irrigate 30,000 hectares of farmland.

The farming area, which usually suffers from severe drought, is a major crop production base in Xigaze.

The project will have two power stations with a combined generation capacity of 42 megawatts. They are designed to generate 85 million kilowatt-hours of electricity each year.