Relief organisations were awaiting clearance from Myanmar's military rulers on Wednesday to access areas of Rakhine State devastated by a deadly cyclone three days ago, and deliver food and medicine to communities in urgent need.

Hundreds of people are estimated to have been killed in the impoverished region after cyclone Mocha on Sunday tore down houses, communication towers and bridges with winds of up to 210 kph (130 mph) and triggered a storm surge that inundated the state capital Sittwe.

Residents contacted by Reuters said no help had arrived even days after the storm and volunteers were digging through debris to search for the missing.

One resident who declined to be identified for safety reasons said about 400 people had died and more were at risk of dying "for not having food, purified water and emergency treatment. There are no ... search and rescue teams."

Rakhine State, with a population of more than three million, is particularly vulnerable, and is home to the persecuted Rohingya Muslims minority that successive governments in predominantly Buddhist Myanmar have refused to recognise.

Some 600,000 Rohingya still live in the state, while more than a million live in sprawling camps in neighbouring Bangladesh, having fled military crackdowns in recent years. Some still embark on perilous boat journeys to Malaysia and Indonesia.

United Nations agencies said they were still awaiting a green light from authorities to assess and distribute supplies in affected areas, some of which were inaccessible due to extensive damage.

"We have established communications channels with all authorities in Myanmar. We have asked for unrestricted access to affected communities," said Pierre Peron, a spokesperson for the United Nations Office for the Coordination of Humanitarian Affairs.

The U.N. Development Programme, the U.N. Children's Fund (UNICEF) and U.N. refugee agency UNHCR also said their requests were pending approval.

"It is important for humanitarian actors to ascertain damage, needs and provide immediate lifesaving assistance, not least as the monsoon season nears," UNHCR spokesperson Reuben Lim Wende said.

State media on Wednesday said junta leader Min Aung Hlaing had visited affected areas in Bagan, another region, and separately met with a UNHCR representative to discuss relief efforts.

It said military vessels and helicopters had transported aid to Rakhine and 21 people, including security force personnel doing rescue work, had died as a result of the storm. A spokesperson for the junta could not be reached.

About 5.4 million people were expected to have been in the storm's path, the majority of whom were considered vulnerable.

(Reporting by Reuters staff, Poppy McPherson in Bangkok; Writing by Kanupriya Kapoor; Editing by Martin Petty & Simon Cameron-Moore)