Bangladesh raised its storm danger signal to the highest level of 10 as a severe and intensifying cyclone churned towards its low-lying coast and was expected to make landfall in the early hours todayy.

Impoverished Bangladesh, hit by cyclones every year, warned that some coastal areas were "likely to be inundated by a storm surge of 1.2 to 1.5 metres above normal because of approaching Cyclone Mora.

The Disaster Ministry ordered authorities to evacuate people from the coast, the ministry's additional secretary, Golam Mostafa, told reporters in Dhaka. About 10 million of Bangladesh's population of 160 million live in coastal areas.

River ferries had suspended operations and fishing boats called in to safety.

"Maritime ports of Chittagong and Cox’s Bazar have been advised to lower danger signal number seven but instead hoist great danger signal number ten (repeat) ten," a government weather bulletin said.

"The coastal districts of Chittagong, Cox’s Bazar, Noakhali, Laxmipur, Feni, Chandpur and their offshore islands ... will come under danger signal number ten (repeat) ten."

Bangladesh is hit by storms, many of them devastating, every year. Half a million people had their lives disrupted in coastal areas such as Barisal and Chittagong in May last year.

It is still recovering from flash floods that hit the northeast, affecting millions of people, in April. Rice prices have reached record highs and state reserves are at 10-year lows in the wake of flooding that wiped out around 700,000 tonnes of rice.

The cyclone formed after monsoon rains triggered floods and landslides in neighbouring Sri Lanka, off India's southern tip, which have killed at least 177 people in recent days, authorities said, with 24 killed in storms in the eastern Indian state of Bihar, either by lightning strikes or under collapsed village huts.