A large number of Rohingya Muslims were killed in Myanmar when Cyclone Mocha struck at the weekend, residents, a relief group and a media outlet said on Tuesday, with substantial damage reported and many areas inaccessible.

Myanmar's strife-torn Rakhine State bore the brunt of Sunday's storm that unleashed winds of up to 210 kph (130 mph) and ripped roofs off homes, and brought a storm surge that inundated the state capital Sittwe.

Non-governmental relief organisation Partners said on Twitter said there were many deaths and injuries, citing its sources on the ground. It posted a video showing damage.

Reuters could not independently verify the number of casualties. Myanmar's state media on Monday reported three people were killed.

"We are scaling up our response effort to provide critical relief supplies like rice and tarps to Rohingya communities affected by Cyclone Mocha as we are able,” Partners said in another post on Twitter.

The western Myanmar region is home to hundreds of thousands of Rohingya, a persecuted minority that successive governments have refused to recognise. More than a million live in sprawling camps in neighbouring Bangladesh, having fled military crackdowns in recent years.

News portal Myanmar Now said 22 Rohingya were killed, citing residents.

Myanmar's state media on Tuesday made no mention of casualties but said junta chief Min Aung Hlaing had visited Sittwe to assess the damage, donate money and give instructions on the response.

Before the storm made landfall on Sunday about 400,000 people were evacuated in Myanmar and Bangladesh.

The UN humanitarian office (OCHA) said about 6 million people in the region were already in need of humanitarian assistance before the storm, among them 1.2 million people internally displaced by ethnic conflict.

A resident in the area, who declined to be identified over concerns for their safety, told Reuters more than 100 Rohingya were killed, based on assessments from multiple villages he said he had visited in the aftermath.

"There are also so many missing people from the storm,” he said. “We didn't receive any help so far.”

Two other residents contacted by Reuters also said a large number of people had been killed, as did a diplomatic source briefed on the situation, who did not provide details.

The storm was one of the worst since Cyclone Nargis swept across parts of southern Myanmar killing nearly 140,000 people in 2008.