Rescue work is expected to continue for a couple of days in rugged hilly terrain with little hope of finding survivors among 37 people missing since Wednesday night.
Pankaj Kavidayal, a rescue official, said 21 of the confirmed 26 dead were members of the Territorial Army.
Troops had been providing security for railway officials because of a decades-old insurgency seeking a separate homeland for ethnic and tribal groups in the area.
More than 250 soldiers, rescuers and police using bulldozers and other equipment were involved in the operation in Noney, a town near Imphal, the capital of Manipur state.
They have been warned of fresh mudslides in the region on Saturday.
Thirteen soldiers and five civilians have been rescued from the debris of the swept away railway station, staff housing and other infrastructure that was being built, Kavidayal said.
Continuous rainfall over the past three weeks has wreaked havoc across India's northeast, taking in eight states and 45 million people, as well as neighbouring Bangladesh.
An estimated 200 people have been killed in heavy downpours and mudslides in states including Assam, Manipur, Tripura and Sikkim, while 42 have died in Bangladesh since May 17.
Hundreds of thousands have been displaced.
Scientists say climate change is a factor behind the erratic, early rains that triggered unprecedented floods.
Monsoon rains in South Asia typically begin in June, but torrential rain has lashed northeastern India and Bangladesh since March this year.
