Pedestrians use umbrellas to shield themselves from the wind and rain in Kolkata, India, Saturday, Nov. 9, 2019. Cyclone Bulbul lashed coastal areas in eastern India and southern Bangladesh overnight, killing 11 people and forcing mass evacuations. File photo: AP Photo/Bikas Das.

New Delhi/Dhaka - Cyclone Bulbul lashed coastal areas in eastern India and southern Bangladesh overnight, killing 11 people, forcing mass evacuations and leaving a trail of destruction in the region, officials said on Sunday.

The cyclone brought heavy rains and winds with speeds of up to 120 kilometres per hour as it made landfall on Saturday night in the Sundarbans, the world's largest mangrove forest between India and Bangladesh, on the coastline of the Bay of Bengal.

In India, one man was killed when a tree fell on him in Kolkata, the capital of West Bengal state, police confirmed.

Six more people died, mostly in incidents of wall collapses in the North 24 Parganas and East Medinipur districts, state disaster officials said.

In the neighbouring state of Odisha, another person died in another incident of a wall collapse, state disaster management chief PK Jena said.

In Bangladesh, the tropical storm killed three people who were hit by falling trees, police officials said.

Bangladesh moved 2.1 million people to safety ahead of the cyclone, state minister for disaster management Enamur Rahman said, while India shifted nearly 125,000 people, mostly in West Bengal state.

Flights to and from the region's main airport at Kolkata were suspended as a precautionary measure.

Bangladeshi forest conservator Moyeenuddin Khan said he had no reports of major damage to the Sundarbans, where the storm made landfall.

"Roofs made of corrugated iron in some of our forest offices ... have blown away and some trees were uprooted," Khan said.

The 140,000-hectare forest, shared between Bangladesh and India, is a UNESCO World Heritage site and home to many rare species, including Bengal tigers.

The storm had moved to the north-east and weakened into a "deep depression" over coastal Bangladesh by Sunday afternoon, with wind speeds of up to 60 kilometres per hour, the Indian Meteorological Department said. It was expected to weaken further by late Sunday night.

Rescue and relief teams have been sent to affected areas to assess the damage, Amalendu Dutta, an official in the state disaster management, said by phone from Kolkata.

"Hundreds of trees and electricity pylons were uprooted. Large numbers of thatched houses and of paddy farms have been damaged," Dutta said.

Jena said roads were being cleared and electricity was being restored in Odisha's affected regions.

Indian Prime Minister Narendra Modi said he has reviewed the situation in eastern India and assured the region of all possible assistance from the central government.

Bangladeshi officials said the storm left crops damaged over vast coastal areas.

"We have asked the local administration to conduct quick assessment into the damages caused by the cyclone," Shahadat Hossain, head of Bangladesh's disaster management department, told dpa by phone.

Standing crops, especially paddy and vegetable plantations, may have been dealt a severe blow, he said, adding that a detailed report on the damage would be available in a week.

Cyclones often form over the Bay of Bengal from April to November, bringing widespread destruction in coastal regions in India and Bangladesh.