Nearly 800,000 people in eastern India have been evacuated from the path of an incoming major cyclone packing winds gusting up to 200 kilometres (125 miles) per hour and torrential rains, officials said on Thursday.

The Indian weather service said Extremely Severe Cyclonic Storm Fani was expected to make landfall on Friday afternoon in Odisha state and barrel northeastwards towards Bangladesh on a pathway that is home to more than 100 million people.

Along with "extremely heavy" rainfall in places, a storm surge of about 1.5 metres (five feet) is "very likely" to inundate some low-lying areas of Odisha, according to the Indian Meterological Department.

A state relief department official told AFP that 780,000 people were moved to safer places overnight from at least 13 districts of Odisha, home to 46 million people, which will bear the brunt of the storm.

"We are expecting more than a million people to move out of the danger zone in next 12 hours," Bishnupada Sethi, Odisha Special Relief Commissioner, told AFP.

Some 3,000 shelters in schools and government buildings have been set up to accommodate more than a million people. More than 100,000 dry food packets are ready to be dropped if needed, reports said.

On Thursday, the storm, which reports said was the biggest to hit eastern India in nearly two decades, was brewing in the Bay of Bengal and moving steadily and ominously towards the shore.

It was predicted to pack sustained wind speeds of 180-190 kph and gusts up to 200 kph, equivalent in strength to a Category 3 to 4 hurricane.

It was expected to make landfall near the Hindu holy town of Puri, a major tourist hotspot.

More than 100 trains have been cancelled in past 48 hours, according to Indian Railways. Three special trains were running from Puri to evacuate pilgrims and tourists.

Authorities have asked tourists to leave coastal areas and avoid unnecessary travel. Special buses have been deployed in Puri and other towns.

Dozens of officials were making announcements on hand-held megaphones across the coastal belt asking residents to leave their homes.

After Odisha, Fani was predicted to head north towards the state of West Bengal and then towards Bangladesh, where authorities were already preparing on Thursday.

Other coastal states south of Odisha like Andhra Pradesh, home to 50 million people, and Tamil Nadu, population some 70 million, were also on standby.

Fishermen have been advised not to venture out. The Indian Navy has also been put on alert.

India's biggest oil and gas producer ONGC has evacuated close to 500 employees from offshore installations and moved drilling rigs to safer locations, the Press Trust of India reported.

The Airports Authority of India also issued an advisory to all the coastal airports to take adequate precautions.

"Heavy rains are expected in all the coastal districts amid fears of flash floods. We are all geared up for the challenge," said Sethi.

'Total destruction'

Forecasters have warned of the "total destruction" of thatched houses, the bending and uprooting of power and communication poles, the "flooding of escape routes" and damage to crops in some areas.

Bangladesh disaster management chief Mohammad Hashim said that 3,600 cyclone shelters had been opened in 13 coastal districts.

The country's weather bureau has told deep-sea fishing vessels to stay near the coast, while inland water transport activities were suspended.

Coastal-area farmers in Bangladesh were instructed to harvest their paddy fields as a surging tide may inundate and ruin crops.

Fani is the fourth major storm to slam into India's east coast in three decades, the last in 2017 when Cyclone Ockhi left nearly 250 people dead and more than 600 missing in Tamil Nadu and Kerala.

The worst cyclone on record in Odisha in 1999, killed almost 10,000 people and caused an estimated $4.5 billion worth of devastation.