India has inaugurated a 9.15km (5.68-mile) bridge over the Lohit river, easily its longest ever, which connects the disputed state of Arunachal Pradesh with the north-eastern state of Assam.
China claims Arunachal Pradesh as its own, and refers to it as "southern Tibet".
Beijing recently strongly objected to India's decision to allow Tibetan spiritual leader Dalai Lama to visit the state and has also protested against the development of military infrastructure there.
But India has defended its right to do so.
"With China getting more and more aggressive, it is time we strengthened our physical infrastructure to defend our territory," India's junior Home Minister Khiren Rijiju, a native of Arunachal Pradesh, told journalists.
Mr Rijiju had earlier said that "Arunachal Pradesh is part of India and that reality will not change, regardless of who likes it or not".
Construction of the Dhola Sadiya bridge began in 2011.
"It was real tough work, a major engineering challenge, and the speed was slightly affected by some compensation issues," said an official from Navayuga Engineering, the company which constructed the bridge.
However, it was completed on schedule.
Apart from the bridge, India is constructing a two-lane trans-Arunachal highway, upgrading a World War Two vintage road and undertaking a further four projects to widen roads.
Another project, to upgrade a chain of advance landing grounds for heavy lift transport aircraft, has also moved at some speed. This is expected to improve India's strategic airlift capabilities.
"We need infrastructure to move up troops and supplies if we have to fight the Chinese and this bridge is a great thing," retired Major General Gaganjit Singh, who has commanded a division in the state, told the BBC.
"India did not develop physical infrastructure in Arunachal Pradesh for two decades after the 1962 war as many stupidly believed the Chinese would use the roads if they attacked again. But now we are on the right track."
India's Home Minister Rajnath Singh has also stressed the importance of developing physical infrastructure in the state, as part of efforts to defend a long border with China.
"We want peace, but peace with honour. We need to be capable of deterring anyone who may think we are weak," Mr Singh told members of the Indo-Tibetan Border Police force that guards parts of the frontier with China.
His remarks followed Beijing's strident protests against the "development of military infrastructure in a disputed province".
India has already raised two mountain divisions and is going ahead with raising a strike corps to beef up its defences against China.
"But troop strength is useless if we don't have the roads and bridges to move them fast when we are threatened. Moving them with heavy equipment quickly to the battlefront holds the key to victory," Major General Singh said.
A military engineer told the BBC that the Dhola-Sadiya bridge was capable of supporting 60-ton battle tanks.
Locals are also excited about the opening.
"It was unimaginable that this crossing could be bridged at a point where six rivers meet, all flowing into the mighty Brahmaputra," Gunjan Saharia, a resident, told the BBC.
"I promise this will not just be a military thing, it will help develop the economy of remote regions of Assam and Arunachal, and it will attract tourists in large numbers," Assam Chief Minister Sarbananda Sonowal said.
The bridge will also reduce travel time by as much as eight hours for communities on either side of the river.
"It will be great for us, as much as it will be great for the army," Dimbeswar Gogoi of Sadiya told the BBC.