Strong gales and heavy rain brought by cyclone Remal lashed the coastlines of India and Bangladesh on Monday, with the storm killing at least 16 people and cutting electricity supply to millions before losing intensity.

The cyclone is the first this year of the frequent storms that have pounded the low-lying coasts of the South Asian neighbours in recent years, as climate change drives up surface temperatures at sea.

Packing speeds of up to 135 kph (84 mph), it crossed the area around Bangladesh's southern port of Mongla and the adjoining Sagar Islands in India's West Bengal late on Sunday, weather officials said, making landfall at about 9 p.m. (1530 GMT) before weakening on Monday morning.

The official death toll mounted in both countries as information arrived from coastal regions.

At least 10 people lost their lives in Bangladesh, disaster management chief Mijanur Rahman told Reuters, without providing details.

Two were killed as they headed to cyclone shelters, Rahman earlier said, adding that authorities will need more time to gauge the full extent of losses.

"People are usually very reluctant to leave their livestock and homes to go to cyclone shelters," he said. "They wait until the last minute when it is often too late."

In India's West Bengal state, four people died due to electrocution, authorities said, taking the death toll in the state to six.

One person was crushed to death by falling concrete in the state capital of Kolkata, while a woman died when a mud home collapsed on the island of Mousuni in the Sundarbans delta.

POWER SUPPLY HIT

Bangladesh shut down electricity supply to some areas in advance to avoid accidents, while in many coastal towns fallen trees and snapped electricity lines further disrupted supply, power ministry officials said.

"We have had no electricity since night, my mobile battery will run out any time," said Rahat Raja, a resident of Bangladesh's coastal district of Satkhira. "By Allah's grace, the cyclone was not as violent as we thought."

Nearly 3 million people in Bangladesh were without electricity, officials added. West Bengal authorities said at least 1,200 power poles were uprooted, while 300 mud huts had been razed to the ground.

Fierce winds also blew the roofs off some tin and thatched houses. The rain and high tides damaged some embankments and flooded coastal areas in the Sundarbans, home to some of the world's largest mangrove forests, which is shared by India and Bangladesh.

Rain flooded roads disrupted travel in Bangladeshi capital Dhaka, where authorities gearing for the storm set up nearly 8,000 cyclone shelters and drafted in 78,000 volunteers.

In Mongla, boatman Shah Alom said he had not seen such a lengthy cyclone in decades. "Usually the storm lasts for a couple of hours, but this one has been going on since last night," he said. "I don't know when it will end."

Rains brought by the storm flooded many streets in Kolkata, television images showed, with reports of wall collapses and at least 52 fallen trees.

Kolkata resumed flights after more than 50 were cancelled from Sunday. Suburban train services were also restored.

Both nations moved nearly a million people to storm shelters, about 800,000 in Bangladesh and roughly 110,000 in India, authorities said.

The storm is expected to move northeast and gradually weaken further into a deep depression by afternoon, bringing more rain to states there, they added.