- Hundreds of people crammed into a school in the city which had been turned into a temporary cyclone shelter.
- Authorities here say more than 500,000 people were evacuated from their homes in this south-eastern stretch of Bangladesh.
A powerful cyclone has hit the coastlines of Bangladesh and Myanmar after intensifying into the equivalent of a category-five storm.
Cyclone Mocha brought with it heavy rain and strong winds, leaving residents in low-lying coastal areas fearful they may lose their homes.
More than 500 bamboo shelters in Cox's Bazar, the world's largest refugee camp, have been destroyed.
Landslides and floods are also hitting the area.
As the storm approached, police patrolled the coastline in the town of Cox's Bazar carrying loudspeakers, urging people to stay indoors.
The streets emptied as the cyclone intensified - the skies darkened, the winds picked up pace and the rains pounded down.
Hundreds of people crammed into a school in the city which had been turned into a temporary cyclone shelter.
Mothers with babies, young children, the elderly and the frail packed into any available space in the classrooms, sleeping on desks and sitting under them.
Authorities here say more than 500,000 people were evacuated from their homes in this south-eastern stretch of Bangladesh.
As many arrived at the shelter in rickshaws and on foot, they brought their livestock - cattle, chickens, goats - as well as mats to sleep on.
They had come from fishing and coastal villages, as many as two hours away, making a difficult choice.
"I didn't want to leave my house," said Sumi Akter, who lives on a riverbank.
Sumi and others we met here say they have lived through other cyclones in recent years and are resigned to the regular pattern of leaving their homes to the mercy of nature.
Storm surges of up to four metres could swamp villages in low-lying areas, Sumi and others here are fearful their homes may be submerged.
"I wish the homes we lived in were built more strongly," she said.
Not too far away from the cyclone shelter, close to a million Rohingya refugees were also feeling impact of the cyclone.
Bangladesh's government does not allow the refugees to leave the camps, nor build permanent structures.
As the cyclone hit, they hunkered down in flimsy bamboo shelters with tarpaulin roofs. Some were moved to community shelters within the camps, which offered little more protection.
Authorities told the BBC that about 500 shelters were damaged by the wind. Trees had also fallen in the camps, while two landslides also caused some damage.
Mizanur Rahman, from the Refugee Relief and Repatriation Commissioner said that as far as he was aware, there were no casualties in the camps as a result of the cyclone.
Forecasters warned Cyclone Mocha could be the most powerful storm seen in Bangladesh in nearly two decades. It also hit neighbouring Myanmar with great force.
Heavy rain and driving winds battered the region as the storm system moved to the coast, with reports of increasing disruption near the city of Sittwe, in Myanmar, from about 13:00 (07:00 GMT).
Electricity and wi-fi connections were disrupted across much of the Sittwe area, where videos showed the tide rising dramatically and carrying debris down flooded streets.
A telecom tower was brought down by the high winds as the cyclone approached. Videos shared on social media also showed roofs being blown off houses and billboards flying off buildings in Yangon amid teeming rain.
Images from the city of Mrauk U showed palm trees bending in the wind, metal roofing sheets being swept into the street and a few people still hurrying to take cover in storm shelters.
Local media reported that a 14-year-old boy was killed by a falling tree in Myanmar's Rakhine State, while there were reports of damaged and collapsed buildings in various parts of Myanmar.
The Bangladeshi meteorological department office said the maximum sustained wind speed within 75km (45 miles) of the centre of the cyclone was about 195km/h (120mph), with gusts and squalls of 215km/h.
Dr MM Malik, a meteorologist at the government storm warning centre in Dhaka, told the BBC that the cyclone's diameter was 520km, which means it will take some time to fully cross the coastline.
In preparation for the storm's arrival, nearby airports were shut, fishermen were ordered to suspend their work and 1,500 shelters were set up as people from vulnerable areas were moved to safer spots.
Cyclone Mocha was predicted to bring a deluge of rain, which can trigger landslides - a serious danger for those who reside in hillside camps, where landslips are a regular phenomenon.
"For a cyclone to hit an area where there is already such deep humanitarian need is a nightmare scenario, impacting hundreds of thousands of vulnerable people whose coping capacity has been severely eroded by successive crises," said UN humanitarian co-ordinator AI Ramanathan Balakrishnan.