NOVA FRIBURGO , Brazil ( Reuters ) ― Brazilian army helicopters stepped up rescue and supply operations Monday in areas hit by floods and landslides that have killed at least 665 people , reaching residents who had been cut off from help for five days . One helicopter team rescued five people in the morning , the Air Force said in a statement , as clearer weather allowed the aircraft to navigate more safely around the craggy terrain north of Rio de Janeiro city . Army helicopters transport rescue personnel to isolated flooded areas in Itaipava , Petropolis , some 100 km from downtown Rio de Janeiro on Monday . ( AFP - Yonhap News ) Hundreds of people are believed to still be in areas at risk of fresh mudslides , some of them cut off from help by smashed roads and bridges while others refuse to leave for fear their houses will be raided by looters . The army is operating four helicopters from a makeshift base on the training ground for Brazil ’ s national soccer team in the town of Teresopolis . “ It ’ s impossible to calculate how many people are still buried , ” Vice Governor of Rio de Janeiro Luis Fernando Pezao told Reuters . “ Our numbers are based on the coroner and the fire department but there are a lot of people still buried . ” Heavy rains last week sparked one of Brazil ’ s worst natural disasters , sending an avalanche of mud , water and rocks plowing through towns and villages in the scenic region . Poorer residents who lived in precarious housing bore the brunt of the carnage . The death toll has risen steadily as rescuers have dug bodies from the wreckage . Authorities have given no estimates of the number of missing , but Folha de Sao Paulo newspaper said Monday that 120 people are unaccounted for . Some residents have complained over what they say has been a slow response by authorities in getting basic supplies to isolated communities and helping people dig out dead relatives and friends . A fresh landslide Sunday near the town of Petropolis killed three people , media reported , highlighting the risks posed by rain forecast for the region in the coming days . In the capital Brasilia , the government sought to fend off criticism over its response by announcing that it would implement a national alert system to warn people in risky areas of approaching natural disasters . The announcement came after the Estado de Sao Paulo newspaper reported that Brazil had failed to meet a series of recommendations on improving disaster preparedness made by the United Nations in 2005 . Citing a letter sent by Brazil ’ s Civil Defense agency to the United Nations last November , it said the government had not yet implemented recommendations such as setting up the alert system and investing sufficiently in infrastructure in risky areas . “ There is a culture in Brazil of waiting for something to happen and then responding to it , ” the head of the Civil Defense agency , Humberto Vianna , was quoted as saying . Still , little criticism has so far been directed at Brazil ’ s new president , Dilma Rousseff , despite her single , brief visit to the disaster zone last week and her decision to spend the weekend far from the devastated region . The federal government has earmarked 780 million reais ( $ 463 . 5 million ) in emergency aid for the region . Brazil ’ s Valor Economico newspaper praised Rousseff ’ s response to the disaster in an editorial Monday , saying she had passed the first test of her presidency by acting rapidly and taking adequate measures .