A US-based pressure group says the lives of thousands of people have been devastated by a giant hydroelectric dam being constructed in Guinea as part of China's Belt and Road initiative.

Human Rights Watch said 16,000 people had been displaced and more than 250 sq km of land flooded.

The displaced are not receiving replacement farmland and are being told to cultivate existing land more intensively or switch to fishing.

The Guinean government, which is constructing the dam in partnership with China, said it is doing all it can to help the displaced find alternative livelihoods.