CHITTAGONG - Thousands of Bangladeshis were left homeless on Sunday after Cyclone Roanu battered the impoverished southern coastal region, ripping apart flimsy houses and killing at least 24 people.

The storm on Saturday ploughed through low-lying villages in the Chittagong and Barisal regions, where residents described seeing metres-high walls of water.

Many Bangladeshis were returning safely home on Sunday after authorities evacuated more than 500,000 to shelters before the cyclone hit, packing winds of up to 88 kilometres (54 miles) per hour.

But officials said thousands of others along the coast had been left stranded in their homes as seawater barrelled through dykes and flooded dozens of villages.

"Before we could realise, the whole village was washed away by a huge wall of water," said Abu Siddique, a councillor from Banshkhali district in Chittagong.

"It came at least six hours early, giving the villagers no time to rush to cyclone shelters. Those who died were caught by a sudden rush of water," he told AFP.

"They (authorities) said the storm surge would be four-feet high but in some places the water that hit our shore was as high as 10 feet (three metres)."

Bangladesh's disaster management chief said thousands of homes were damaged or destroyed and 24 people had been killed in total.

About half of those who died were from the Chittagong region which bore the brunt of the storm, Disaster Management Department head Reaz Ahmed told AFP.

"Some 80,000 tin-and-mud-built homes were damaged by the storm in the coastal regions including 23,000 homes which were completed knocked down," Ahmed said.

Authorities were sending relief supplies including rice and other dry food to affected areas, where many poor residents already have very little and scratch a living as small fishermen or farmers.

Television footage showed villagers sitting helplessly in front of their flattened houses.

"In a moment my home was destroyed," an unnamed villager in Bhola island off the Barisal coast told the private Independent Television channel.

A week of extreme weather has wreaked havoc across South Asia, with Sri Lanka pounded by the heaviest rains in 25 years triggering severe floods and landslides.

More than 80 villages in Bangladesh's Barisal were flooded after a rain-swollen dam burst and forced residents to flee, the Daily Star newspaper said on Sunday.

Seawater also gushed through shops and warehouses in the commercial hub and main port city of Chittagong, police and industry officials said.

"Food supplies worth one billion taka ($12.5 million) was damaged after seawater entered our warehouses," Chittagong Chamber of Commerce and Industry president Mahbubul Alam told AFP.

Flights at Chittagong's international airport resumed after two days of shutdown from the storm which weakened after making land.

The government said it was deploying a minister and top disaster officials to the worst-hit areas to assess the damage.

Bangladesh is regularly battered by cyclones which form in the Bay of Bengal. Cyclone Aila in 2009 killed 300 people while Cyclone Sidra claimed 4,000 lives in 2007.

Earlier this month lightning strikes killed an unprecedented 59 people in Bangladesh in three days as tropical thunderstorms hit the country before the annual monsoon, which runs from June to September.