Cyclone Bulbul hit coastal areas of eastern India and southern Bangladesh overnight, killing 11 people and forcing tens of thousands to flee their homes, officials said Sunday.

The cyclone triggered heavy rains and winds of up to 120 km per hour after it hit the world's largest mangrove forest between Bangladesh and India on the coast of the Bay of Bengal.

One person died in India when a tree fell on him in Kolkata, the capital of West Bengal on Saturday evening, police said.

Six more people died, most in wall collapses in North 24 Barganas and East Medinpur, state disaster management officials said.

In Odisha state, another person died after a wall collapsed, said disaster management chief PK Gina.

In Bangladesh, the cyclone killed three people after falling trees.

The two countries evacuated hundreds of thousands of coastal residents to safety before the cyclone arrived as a precaution. Bangladesh has evacuated 2.1 million people. While India has transported about 125,000 people, mostly from West Bengal, work has stopped at the area's airport in Calcutta as a precaution.

The Indian Meteorological Agency said the cyclone had moved north-east and had dropped to a "low" strength over the coast of Bangladesh by Monday evening, reaching a speed of 60 kilometers per hour.