The areas in and around Itanagar, the capital of Arunachal Pradesh, had been hit by two days of heavy rains.
Payeng said there were reports of at least two vehicles falling down a gorge on the city's outskirts.
In the neighbouring state of Assam flash floods caused by the monsoon hit 120 villages, displacing about 30,000 people.
Monsoon rains usually hit the country from June to September.