The populous Indian state of West Bengal took the brunt of Cyclone Amphan, which barrelled out of the Bay of Bengal with gusting winds of up to 185 km per hour (115 mph) and a storm surge of around five metres.
High winds and torrid rains pounded coastal villages and cities, bringing down power lines, uprooting trees and inundating homes.
West Bengal Chief Minister Mamata Banerjee monitored the extremely severe cyclonic storm Amphan at Nabanna control room in Howrah.
She said at least 10 people had died in the state, and two districts been completely battered by one of the strongest storms to hit the region in several years.
Trees and polls fell
In West Bengal's capital city, Kolkata, strong winds upturned cars and felled trees and electricity poles. Parts of the city were plunged into darkness.
Authorities had scrambled to evacuate more than three million people from low-lying areas, but the task was complicated by the need to prevent the spread of coronavirus.
Cyclones frequently batter parts of eastern India and Bangladesh between April and December, often forcing the evacuations of tens of thousands and causing widespread damage.
Satellite image released by NASA shows powerful Cyclone Amphan over the Bay of Bengal in India on May 20.
In Bangladesh officials confirmed six deaths including a five-year-old boy and a 75-year-old man, both hit by falling trees, and a cyclone emergency volunteer who drowned.
Expected to weaken
The cyclone is expected to weaken as it moves north and northeast, and recede to a tropical depression by midday Thursday, the Indian Meteorological Department said.
Bangladesh officials were particularly concerned about the damage to the Sunderbans, a UNESCO world heritage site famed for its mangrove forest and tiger population, which they said bore the brunt of the cyclone.