The United States Geological Survey said the quake hit at a depth of 34 km with its epicentre near Dhekiajuli town, 140 km north of Assam's main city, Guwahati.
Earlier the European Mediterranean Seismological Centre (EMSC) put the quake magnitude at 6.2.
"Big earthquake hits Assam. I pray for the well-being of all and urge everyone to stay alert. Taking updates from all districts," Assam chief minister Sarbananda Sonowal said.
Residents said there were cracks on the wall in some houses and on floors. People stood outside on the street, anxious about fresh tremors. "Never seen such huge vibrations in my life," said Jyotishman Deka, a 20-year-old engineering student.
Strong tremors were repeatedly felt in several north eastern parts of India and neighbouring Bhutan, forcing hundreds of people to run out of their homes, according to a Reuters witness.
India's National Disaster Management Agency was assessing reports of destruction and casualties after the quake, said an official at the agency who asked to remain unidentified.
New Caption: Residents are seen after vacating their houses following an earthquake in Nagaon district in the northeastern state of Assam, India, April 28, 2021. REUTERS