PORT BLAIR, India — India and Japan are in talks to collaborate on upgrading civilian infrastructure in the Andaman and Nicobar Islands, an Indian archipelago seen as a critical asset to counter China’s efforts to expand its maritime reach into the Indian Ocean.

The first project being discussed is a modest one: a 15-megawatt diesel power plant on South Andaman Island, as described in a proposal submitted late last month to the Japanese Ministry of Foreign Affairs.

But the collaboration signals a significant policy shift for India, which has not previously accepted offers of foreign investment in the archipelago. The Andaman and Nicobar Islands are northwest of the Strait of Malacca, offering control of a so-called choke point that is one of China’s greatest marine vulnerabilities.

It is testimony to the unfolding relationship between India and Japan, which is also funding a $744 million road building project in the northeastern Indian border regions of Mizoram, Assam and Meghalaya. Like the Andaman and Nicobar chain, the northeastern region is a strategic area that has remained relatively undeveloped because of its separation from the mainland.