Hundreds of thousands of people were evacuated from the coasts of Myanmar and Bangladesh on Saturday as the region's most powerful cyclone for over a decade churned across the Bay of Bengal.

Cyclone Mocha was packing winds of up to 240 kilometres per hour, according to the Zoom Earth website, which classed it as a Super Cyclone.

A dangerous category four on the Saffir-Simpson scale, it was expected to weaken before making landfall on Sunday morning between Cox's Bazar, where nearly one million Rohingya refugees live in camps largely made up of flimsy shelters, and Sittwe on Myanmar's western Rakhine coast.

However Bangladeshi authorities moved 190,000 people in Cox's Bazar and nearly 100,000 in Chittagong to safety, divisional commissioner Aminur Rahman said late on Saturday.

"They were evacuated to nearly 4,000 cyclone shelters," he said.

Forecasters in Dhaka were predicting a storm surge up to nearly four metres high, which could inundate low-lying coastal and riverine villages.

On the other side of the border, Sittwe residents piled possessions and pets into cars, trucks and tuk-tuks and headed for higher ground on Saturday.

Shops and markets in the town of about 150,000 people were shuttered, with many locals sheltering in monasteries.

Myanmar's junta authorities were supervising evacuations from villages along the Rakhine coast, state media reported on Friday.

Myanmar Airways International said all its flights to Rakhine state had been suspended until Monday.

The Myanmar Red Cross Society said it was "preparing for a major emergency response." (AFP)