China has approved the construction of what will be the world's largest hydropower dam, kicking off an ambitious project on the eastern rim of the Tibetan plateau that could affect millions downstream in India and Bangladesh.

The total cost of the dam could go beyond 1 trillion yuan (about $137 billion), making it the most expensive infrastructure project ever built in the world.

Beijing has approved plans to dam a gorge in the Himalayas that is three times as deep as the Grand Canyon, despite concerns about the impact on Tibet and India.