ILIGAN, Philippines (AP) -- Tropical Storm Washi blew away Sunday after devastating a wide swath of the southern Philippines with flash floods that killed at least 521 people as they slept and turned two coastal cities into a muddy wasteland filled with overturned cars and uprooted trees.

With nearly 500 people missing, Defense Secretary Voltaire Gazmin and top military officials were to fly to the worst-hit city of Cagayan de Oro to help oversee search-and-rescue efforts and deal with thousands of displaced villagers, as the weather began to clear and floodwaters receded. Among the items urgently needed are coffins and body bags, said Benito Ramos, who heads the government's disaster-response agency.

``It's overwhelming. We didn't expect these many dead,'' Ramos said.

Edmund Rubio, a 44-year-old engineer, said he, his wife and two children scrambled to the second floor of their house in Iligan city as raging floodwaters engulfed the first floor, destroying his TV set and other appliances and washing away his car and motorcycle.

Amid the panic, he heard a loud pounding on his door as his neighbors living in nearby one-story houses pleaded with him to allow them into one of his second-floor rooms. He said he brought 30 of his neighbors into the safety of the second floor of his house, which later shook when a huge, floating log slammed into it.

``It's the most important thing, that all of us will still be together this Christmas,'' Rubio told The Associated Press. ``There was a nearby shantytown that was smashed by water. I'm afraid many people there may not have been as lucky as us.''

Army officers reported unidentified bodies piled up in morgues in Cagayan de Oro, where electricity was restored in some areas, although the city of more than 500,000 people remained without tap water.

Philippine Red Cross Secretary General Gwendolyn Pang told the AP that at least 521 people had died in the floods, mostly children and women, and that 458 others were reported missing.

The death toll will most likely rise because many villages remain isolated and unreached by overwhelmed disaster-response personnel. The worst-hit cities were Cagayan de Oro, where at least 239 people died, and nearby Iligan, where Red Cross aid workers reported 195 dead, Pang said.

``Our fear is there may have been whole families that perished so there's nobody to report what happened,'' Pang said. ``Many areas remain isolated and strewn with debris and unreached by rescue teams.''

Tropical Storm Washi started to blow away toward the South China Sea on Sunday after slamming into the western province of Palawan, allowing the weather to clear and disaster-response contingents to intensify search-and-rescue work.

Most of the victims were asleep Friday night when raging floodwaters cascaded from the mountains with logs and uprooted trees after 12 hours of rain from the late-season tropical storm in Mindanao. The region is unaccustomed to the typhoons that are common to the north of the Philippine archipelago.

Both Iligan, a bustling industrial center about 485 miles (780 kilometers) southeast of Manila, and Cagayan de Oro were filled with scenes of destruction and desperation.

A swollen river sent floodwaters gushing through neighborhoods that do not usually experience flooding. A man floated in an inner tube in muddy water littered with plastic buckets, pieces of wood and other debris. Ten people in one home stood on a sloping roof, waiting for rescuers even as water still flooded the lower floors.

Local television footage showed muddy water rushing in the streets, sweeping away all sorts of debris. Thick layers of mud coated streets where the waters had subsided. One car was thrown over a concrete fence and others were crushed and piled atop each other in a flooded canal.

Benito Ramos, who heads the government's Office of Civil Defense, attributed the high casualties in Mindanao ``partly to the complacency of people because they are not in the usual path of storms'' despite four days of warnings by officials that one was approaching.

Thousands of soldiers and hundreds of local police, reservists, coast guard officers and civilian volunteers were mobilized for rescue efforts, but they were hampered by the flooded-out roads and lack of electricity.

Authorities recovered bodies from the mud after the water subsided. Parts of concrete walls and roofs, toppled vehicles and other debris littered the streets.

Rescuers in boats rushed offshore to save people swept out to sea. In Misamis Oriental province, 60 people were plucked from the ocean off El Salvador city, about six miles (10 kilometers) northwest of Cagayan de Oro. Coast guard boats and other rescuers were scouring the waters off Iligan for survivors or bodies that may have been swept away to sea.

In just 12 hours, Washi dumped more than a month of average rains on Mindanao. Forecaster Leny Ruiz said records show that storms that follow the same path as Washi come only once in about every 12 years.

U.S. Secretary of State Hillary Rodham Clinton said in a statement that the Obama administration offered its ``deepest condolences'' for the devastation in the southern Philippines.

``The U.S. government stands ready to assist Philippine authorities as they respond to this tragedy,'' the statement said. ``Our thoughts and prayers are with all of those affected.''