Hardest hit in the Philippines was Leyte Island, where regional Police Chief Elmer Soria said the provincial governor had told him there were about 10,000 dead, primarily from drowning and collapsed buildings. Most were in Tacloban, the provincial capital of about 200,000 people that is the biggest city on the island.
Reports also trickled in indicating deaths elsewhere on the island.
On Samar Island, Leo Dacaynos of the provincial disaster office said 300 people were confirmed dead in one town and another 2,000 were missing, with some towns yet to be reached by rescuers. He pleaded for food and water, adding that power was out and there was no cellphone signal, making communication possible only by radio.
Reports from other affected islands indicated dozens, perhaps hundreds more deaths.
With communications still knocked out in many areas, it was unclear how authorities were arriving at their estimates of the number of people killed, and it will be days before the full extent of the storm is known.
"On the way to the airport, we saw many bodies along the street," said Philippine-born Australian Mila Ward, 53, who was waiting at the Tacloban airport to catch a military flight back to Manila, about 580 kilometers (360 miles) to the northwest. "They were covered with just anything — tarpaulin, roofing sheets, cardboard." She said she passed "well over 100" bodies.
In one part of Tacloban, a ship had been pushed ashore and sat amid damaged homes.
Haiyan inflicted serious damage to at least six of the archipelago's more than 7,000 islands, with Leyte, Samar and the northern part of Cebu appearing to bear the brunt of the storm. About 4 million people were affected by the storm, the national disaster agency said.
Video from Eastern Samar province's Guiuan township — the first area where the typhoon made landfall — showed a trail of devastation. Many houses were flattened and roads were strewn with debris and uprooted trees. The ABS-CBN video showed several bodies on the street, covered with blankets.
"Even me, I have no house, I have no clothes. I don't know how I will restart my life, I am so confused," an unidentified woman said, crying. "I don't know what happened to us. We are appealing for help. Whoever has a good heart, I appeal to you — please help Guiuan."
The Philippine National Red Cross said its efforts were hampered by looters, including some who attacked trucks of food and other relief supplies it was shipping to Tacloban from the southern port of Davao.
Tacloban's two largest malls and grocery stores were looted, and police guarded a fuel depot. About 200 police officers were sent into Tacloban to restore law and order.
With other rampant looting reported, President Benigno Aquino III said he was considering declaring a state of emergency or martial law in Tacloban. A state of emergency usually includes curfews, price and food supply controls, military or police checkpoints and increased security patrols.
The massive casualties occurred even though the government had evacuated nearly 800,000 people ahead of the typhoon.