DHAKA/KOLKATA (Reuters) - Strong winds and heavy rain pounded the coastal regions of Bangladesh and India as severe cyclone Remal made landfall late on Sunday, leaving millions without electricity after power poles fell and some trees were uprooted by gusty winds.

The storm crossed the coastal regions of Bangladesh's Mongla port and the adjoining Sagar Islands in India's West Bengal state with wind speed measuring up to 135 kmph (about 84 mph), the India Meteorological Department (IMD) said.

The landfall process began around 9 pm local time in India on Sunday and continued for about five hours, the regional meteorological office in Kolkata said.

One person was killed in the major metropolitan city of Kolkata when concrete chunks fell on him during the peak of the storm, police said. There was damage to thatched huts and mud houses in the coastal areas of both countries as authorities waited to ascertain the full scale of losses.

The low-lying coasts of South Asian neighbours Bangladesh and India have experienced frequent severe storms in recent years as climate change forces a rise in sea surface temperatures. Remal is the year's first cyclone in the region.

Bangladesh moved about 800,000 people from the port areas of Mongla and Chittagong and nine coastal districts to storm shelters from Sunday afternoon. As many as 110,000 people were also taken to shelters in India.

Dhaka set up nearly 8,000 cyclone shelters and mobilised 78,000 volunteers ahead of the storm while the Indian navy said it had kept ships, aircraft, divers and medical supplies on standby for deployment if required.

Authorities in Bangladesh shut down electricity supply to many areas in advance to avoid accidents while many coastal towns were left in the dark as fallen trees and broken lines disrupted supply, power ministry officials said.

Arup Biswas, the minister for power in West Bengal government, said the power infrastructure was heavily battered. Reports of at least 356 uprooted electricity poles and damage to scores of transformers were received during the first hour of the landfall process, he added.

More than 50 international and domestic flights had to be cancelled in Kolkata city as operations remained suspended since Sunday noon. Bangladesh also suspended operations at Mongla and Chittagong ports.

The river embankments in the Sunderbans delta, the largest mangrove forest in the world, shared by India and Bangladesh, suffered heavy damage with high tides breaching protective embankments at many places.

Kolkata, like the state's coastal belt, was also lashed by heavy rains. Water logging was reported in many parts, according the police officials. At least six trees were uprooted, which blocked roads, while there were also some reports of house collapses, police added.

The cyclone also brought heavy rains to Bangladesh capital Dhaka, causing flooding of roads and severely impacting commuters.

(Writing by Sudipto Ganguly; editing by Michael Perry)

By Ruma Paul and Subrata Nag Choudhury