At least 70 people died and more than 270,000 were driven from their homes in the wake of Tropical Storm Ketsana, according to the country’s National Disaster Coordinating Council (NDCC).
Tens of thousands of families were affected in the Philippine capital Manila and in at least 24 other provinces and cities on the northern island of Luzon on 26 September. More than 40,000 people are in evacuation centres.
Locally known as Ondoy, the storm caught rescuers and emergency response teams off-guard, officials said, with many residents trapped on their rooftops well into the evening.
With wind speeds of up 100 km per hour, the storm dumped heavy rains over large parts of Luzon, including Metropolitan Manila, a mega-city of some 15 million inhabitants. Some reports estimate that up to 80 percent of the capital is still under water.
The continuous heavy rains also forced authorities to release waters from two dams just north of Manila that were threatening to overflow.
The major rivers of Tumana and Marikina, which cut through heavily populated urban areas in the northern and eastern parts of the city, overflowed their banks, triggering a sudden rush of water that submerged entire houses in a matter of hours.
AP video report on flooding in Manila
Rescuers and residents trapped
As the storm happened on a weekend, response efforts were slow and hard to coordinate as government offices were closed and emergency and relief workers were trapped in their own homes.
"I am appealing for help. Please send rescuers, rubber boats and other transportation to help us. Many people are trapped on rooftops and we have not had any help yet," Arnaldo Cando, a village chief in the district of Novaliches in Quezon city, north of Manila, told a local television network late on 26 September before his line was cut off.
Cristine Reyes, a resident in the eastern city of Marikina, said she, her mother and two toddlers were stranded on the second floor of their two-storey family home.
"Please come and get us. The water is now at the top of the staircase and about to enter the room. My mother does not know how to swim and the children are crying," a near-hysterical Reyes said.
Flood waters were so high that all she could see outside her window were the tops of trees jutting out above the water, she said.
"We have been marooned here since one in the afternoon. The rain has not stopped and soon we will be under water," she said.
Storm Ketsana affected tens of thousands of families in the Philippine
capital Manila and in at least 24 other provinces and cities on the
northern island of Luzon
Relief work challenges
Gwendolyn Pang, chairwoman of the Philippine National Red Cross, said emergency relief officials were trying to reach affected areas, but with many roads rendered impassable and major intercity highways turned into raging rivers, it was difficult to get logistical support.
"We have deployed our people in the field, but even going to the areas you would need to have vehicles and trucks to bring rubber boats. The trucks too couldn't get past the flooded areas, and we have been trying to find a way to get there," Pang told IRIN on 26 September.
"We are also requesting for choppers, but have not yet found big ones that can carry really heavy boats. Many were caught by surprise by the fast-rising water."
She said many people were also caught in the floods while on the road with their families and in some areas of central Manila vehicles were totally submerged. She added that that the release of water from the dams and Manila's outdated drainage system clogged with garbage may have also contributed to the flooding.
"Communication lines too have become very challenging, and electricity and lights have gone out in some areas. Our goal now is to really mobilize relief and support. There are so many damaged resources in so many areas," Pang said. She called on civilians and the public not affected by the floods to help in the effort.
“State of calamity”
Defence Secretary Gilberto Teodoro declared a "state of calamity" in 24 provinces and cities - giving local governments quick access to emergency funding for their respective rescue operations.
One of the three airport terminals in Manila was forced to cancel and divert flights after the flooding disrupted its electricity network.
According to Nathanial Cruz, the country’s chief state weather forecaster, the total rainfall for the day was the highest in 42 years.
The storm dumped 341 millimeters of water in one day, breaking the previous record of 334 millimeters on a day in June 1967.
"We experienced an extreme weather event today," Cruz said.