BEIJING — China plans to extend by 2020 a railroad on the high trans-Himalayan plateau of Tibet to the borders of India, Bhutan and Nepal, according to a report in People’s Daily, the official mouthpiece of the Chinese Communist Party.

The extension would lengthen a 157-mile rail route that is expected to open next month from Lhasa, the Tibetan capital, to Shigatse, the traditional seat of the Panchen Lama, a revered spiritual leader. In 2006, China opened the first railway to Tibet, linking Lhasa to China via the province of Qinghai.

The planned lengthening was criticized by Tibet advocates who said it would bring too many ethnic Han migrants to Lhasa and other Tibetan areas. The Wednesday report in People’s Daily cited Yang Yulin, deputy head of the railways administration in Tibet, saying that two additional rail lines would be added from Shigatse — one to Yadong, a point near the Indian and Bhutan borders, and one to Jilong, an area near the border with Nepal.

China and India have a long-running dispute over their Himalayan border. Two areas are in contention: one in the Aksai Chin area of China, which abuts the Ladakh region of India, in the western Himalayas; and the other in the Indian state of Arunachal Pradesh, in the east. Of the two, the dispute over Arunachal Pradesh is more contentious.