The Mexican army and Oaxaca state's civil protection department Tuesday began the rescue work in Oaxaca state, where a landslide buried hundreds of houses. Mexican President Felipe Calderon said via Twitter that the army had reported 'serious damage,' but perhaps not as bad as previously feared. The landslide occurred on early morning Tuesday in Santa Maria Tlahuitoltepec in Oaxaca. A commander of the National Defense Army and 30 troops have arrived on foot, as helicopters couldn't land due to weather conditions, Calderon said. Some 50 troops of the navy have also been dispatched to the place in four vehicles to join the rescue teams. Meanwhile, a plane with 20 troops aboard has taken off from Oaxaca's air base to the scene of the landslide, carrying three search and rescue dogs to find victims buried under the mud. According to Oaxaca's governor Ulises Ruiz, seven deaths have been confirmed till now. But authorities estimated that at least 500 people remain buried under the mud, and the death toll could increase as the rescue work proceeds. 