* Cyclone kills hundreds, uproots thousands
* Houses flattened by huge rocks, mudslides
* Storm hit parts of Mozambique, Malawi, Zimbabwe
* Relief agencies in push to deliver aid
* Hundreds of thousands may be affected (Recasts, adds fresh details)
By Emma Rumney
BEIRA, Mozambique, March 22 (Reuters) - Shortages of water and food stoked frustrations in Mozambique's Beira city on Friday as a swathe of southern Africa scrambled for survival following a powerful cyclone that killed hundreds of people and may have affected hundreds of thousands more.
Cyclone Idai battered Beira, a low-lying port city of 500,000 residents, with strong winds and torrential rains last week, before moving inland to neighbouring Zimbabwe, where it flattened homes and flooded communities, and Malawi.
Idai killed 242 people in Mozambique and 259 in Zimbabwe, and numbers were expected to rise, relief agencies and officials said. In Malawi, 56 died in heavy rains before the onset of Idai, officials there said.
In Zimbabwe's Coppa Rusitu Valley, a township in Chimanimani, near the Mozambican border, hundreds of homes were flattened by large rocks and mudslide from a nearby mountain, burying some residents, who never stood a chance as the cyclone unleashed its fury at night when most were sleeping.
Relatives and rescuers were digging through the debris, hoping to find bodies, but some of the rocks were so big they need blasting, a Reuters witness said. Most people lost relatives, workmates or friends in the township, which also housed government workers, including police.
President Emmerson Mnangagwa on Thursday night said he had come face to face with horrific accounts of people grieving the loss of family and friends in Chimanimani.
Some survivors have taken refuge at churches and centres offering temporary shelter as they deal with the trauma of their losses while private citizens, international aid agencies and the government rushed humanitarian aid to affected areas.
DOCKING TERMINALS DAMAGED
Energy Minister Joram Gumbo said the pipeline bringing fuel from Beira had not been affected by the cyclone but the docking terminals at Beira port had been damaged.
He said Zimbabwe had 62 days supply of petrol and 32 days for diesel, which is in short supply and has led to long queues in the capital. In Mutare city, near Mozambique, diesel shortages were worse, according to a Reuters witness.
"It is the docking terminals at Beira port in Mozambique which were damaged not the pipeline itself," Gumbo said told state power company officials.
Around 15,000 people needed rescuing in Mozambique, Land and Environment Minister Celso Correia said, either by being airlifted out or getting aid dropped to them to survive.
U.N. humanitarian spokesman Jens Laerke told a regular U.N. briefing in Geneva the world body was working with planning figures of 600,000 people affected by the cyclone in Mozambique and 840,000 in Malawi. On Zimbabwe, he had heard from relief agencies an operational figure of 250,000 affected people.
Briefing his team late on Thursday night, Connor Hartnady, rescue operations task force leader for Rescue South Africa, said Beira residents were becoming fed up with shortages.
"There have been three security incidents today, all food related," he told his team, without giving further details.
Cartnady also said a group of 60 people had been discovered trapped by flood water in an area north of Beira during a reconnaissance flight. Rescue teams and the government were deciding how best to help them, he said, either by airlifting them to safety or dropping supplies.
RIVER BANKS BURST
Commenting on Beira, Laerke said if people were desperate to get aid, that should be treated as part of the community response and not as a security matter.
"These are desperate people," Laerke said. "I don't think anybody would blame a desperate mother or father who have children who do not have clean water to drink or food to eat who grab it from wherever they find it in a shop."
The storm's rains caused the Buzi and Pungwe rivers, whose mouths are in the Beira area, to burst their banks.
Roads into Beira were cut off by the storm, and most of the city remains without power. The Red Cross has estimated 90 percent of the city was damaged or destroyed in the storm.
Zimbabwe's Ministry of Information said at least 30 students, two headmasters and a teacher from three schools were missing in the eastern region of the country. (Reporting by Emma Rumney; Additional reporting by MacDonald Dzirutwe in Harare, Philimon Bulawayo in Chimanimani, Zimbabwe,; Editing by Tiisetso Motsoeneng and Raissa Kasolowsky, William Maclean)
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