Indian Prime Minister Narendra Modi, marking three years in power, on Friday inaugurated the country's longest bridge that spans the vast Brahmaputra River in the northeastern state of Assam.

The 9.15 km (5.7 mile) Dhola-Sadiya bridge, strong enough to carry a 60-tonne battle tank, will reduce travel times from Assam to the frontier state of Arunachal Pradesh whose territory is partly claimed by China.

‘The inauguration of the bridge marks the end of a long wait for the people of this area,’ Modi's office quoted him as saying in a speech, adding the bridge ‘opens the door for economic development on a big scale’.

Modi led his Bharatiya Janata Party (BJP) to a landslide victory in 2014. He remains popular - his party swept Uttar Pradesh, India's most populous state, in a recent state election and looks on track to win re-election in 2019.

The 66-year-old prime minister has made upgrading India's infrastructure a priority, also setting up a ministry to develop India's remote northeast beyond the so-called Chicken's Neck - a narrow strip of territory around Bangladesh.

Modi's trip to Assam, during which he will deliver a public address later in the day, rounded off a week of festivities and briefings to highlight his government's achievements. He embarks on a European tour next week.