NEW DELHI, Dec. 25 (Xinhua) -- Indian Prime Minister Narendra Modi inaugurated the country's longest rail-cum-road bridge, Bogibeel Bridge, Tuesday in northeastern state of Assam, officials said.

The bridge has been built over river Brahmaputra in Dibrugarh district, about 446 km northeast of Dispur, the capital city of Assam.

"The inauguration of Bogibeel Bridge is a historic feat and I am glad to be here in Assam, among you all on this special day," Modi said in his address.

"The Bogibeel Bridge is a lifeline for the people of Assam. It has enhanced connectivity between Assam and other parts of the nation."

Officials said the bridge has a two-line railway track on the lower deck and a three-lane road on the top deck.

The 4.9-km bridge is Asia's second longest rail-cum-road bridge and constructed with around 35,400 metric tonnes of steel.

"Steel Authority of India Limited (SAIL) has supplied TMT rebars, plates and structural for this bridge, which has composite welded steel truss girders in its structures," a spokesman of the Ministry of Steel said.

The bridge, according to officials, has a serviceable period of 120 years.

Modi also flagged off the first passenger train over the bridge.