The most powerful cyclone in nearly two decades is barreling toward the coasts of eastern Bangladesh and Myanmar, forecasters warned Saturday.

After brewing in the Bay of Bengal for days, Cyclone Mocha was packing winds of up to 220 kilometers per hour (136 miles) — equivalent to a category four hurricane — as it approached the two Asian countries.

Mocha is expected to weaken before making landfall on Sunday between Cox's Bazar, a southeastern border district of Bangladesh, and Sittwe on Myanmar's western Rakhine coast, Bangladesh's Meteorological Department said in a bulletin.

Rohingya refugees face more misery

Cox's Bazar is where more than a million Rohingya refugees live in flimsy shelters — most having fled a military-led crackdown in Myanmar in 2017.

Bangladeshi authorities have banned the Rohingya from constructing permanent concrete homes, fearing it may incentivize them to settle permanently rather than return to Myanmar.

"All the Rohingyas in the camps are at risk," Bangladesh's deputy refugee commissioner Shamsud Douza told Agence France-Presse.

Authorities in Bangladesh began evacuating refugees from "risky areas" to community centers, while hundreds fled a nearby island.

"We are focusing on saving lives," said Mohammad Shamsud Douza, a Bangladesh government official responsible for refugees. "People who are at risk of landslides will be evacuated."

According to the United Nations, more than six million people need humanitarian assistance in the storm's path in Myanmar alone.

The World Food Programme said it was preparing food and relief supplies that could help more than 400,000 people in Rakhine state and surrounding areas for a month.

Some people in Rakhine's capital Sittwe were either leaving their homes to seek shelter on higher ground or moving further inland, a resident said.

Myanmar has been in chaos since the military seized power two years ago. A resistance movement is fighting the junta on multiple fronts after a bloody crackdown on protests.

Strongest storm in decades

Meteorologists said Mocha was the most powerful storm since Cyclone Sidr, which hit Bangladesh's southern coast in November 2007, killing more than 3,000 people and causing billions of dollars in damage.

Another storm in 2008, Cyclone Nargis, killed more than 100,000 people after hitting southern Myanmar.

Forecasters expect the cyclone to bring a deluge of rain, which can trigger landslides.

The storm is also predicted to unleash a storm surge up to four meters (13 feet) high, which can inundate low-lying coastal and river villages.

Panic has also gripped some 8,000 people in Bangladesh's southernmost island of Saint Martin's with the tiny coral outcrop — one of the country's top resort districts — right in the storm's path.

Officials said around 1,000 Saint Martin's islanders have left, moving 250 boats to Teknaf to try to prevent them from being washed away.

Operations were suspended at the country's largest seaport, Chittagong, with boat transport and fishing activities also halted.