India Prime Minister Narendra Modi has inaugurated one of the most ambitious and strategic railway projects the nation has ever built.

Modi visited the Chenab bridge on Friday with tight security, waving an Indian tri-colour flag before boarding a test train that passed through picturesque mountains and tunnels to reach an inauguration ceremony for another high-elevation bridge named Anji.

Prime Minister Narendra Modi made his first visit to Kashmir on Friday since a conflict with arch-rival Pakistan, opening a strategic railway line to the contested region he called "the crown jewel of India".