It will be days before the full extent of damage is assessed. But the mayor of Tacloban, the first city hit by the typhoon, says it is possible that up to 10,000 people there died in the storm.
The storm left corpses hanging from tree branches, scattered along sidewalks and among flattened buildings. In its aftermath, looters have raided grocery stores and gas stations in search of food, fuel and water.
The Philippine interior secretary says "all systems, all vestiges of modern living - communications, power, water - all are down."
A massive relief operation is underway, but the Philippine National Red Cross says its efforts are being hampered by looters.
President Benigno Aquino III says he's considering declaring a state of emergency or martial law.
President Barack Obama issued a statement regarding Super Typhoon Haiyan on Sunday, saying, "Michelle and I are deeply saddened by the loss of life and extensive damage done by Super Typhoon Yolanda. But I know the incredible resiliency of the Philippine people, and I am confident that the spirit of Bayanihan will see you through this tragedy. The United States is already providing significant humanitarian assistance, and we stand ready to further assist the Government's relief and recovery efforts. Our thoughts and prayers go out to the millions of people affected by this devastating storm."
The United Nations estimates that 9.5 million people have been affected by the typhoon
Hundreds of thousands are thronging relief centers, desperate for the necessities.
About 90 U.S. Marines have arrived from Okinawa in Japan with supplies for victims of the storm and to help in search and rescue efforts.
But with so much of the Philippines still flooded, with electricity and communication cut, and so many roads choked off by debris, the sufferings of millions of storm victims are just beginning.
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(The Associated Press contributed to this report)