As many as 10,000 people are believed to have died in one Philippine city alone when one of the worst storms on record sent giant sea waves, washing away homes, schools and airport buildings.
Ferocious winds ravaged several central islands, burying people under tons of debris and leaving corpses hanging from trees.
Regional police chief Elmer Soria said he was briefed by Leyte provincial governor Dominic Petilla and told there were about 10,000 deaths in the province, mostly by drowning and from collapsed buildings. The governor's figure was based on reports from village officials in areas where Typhoon Haiyan struck on Friday.
Tacloban city administrator Tecson Lim said that the death toll in the city alone "could go up to 10,000". Tacloban is the Leyte provincial capital of 200,000 people and the biggest city on Leyte Island.
On Samar Island, facing Tacloban, Leo Dacaynos of the provincial disaster office said 300 people were confirmed dead in Basey town and another 2,000 missing.
He said the storm surge caused sea waters to rise 20 feet when Typhoon Haiyan hit, before crossing to Tacloban.
There are still other towns on Samar that have not been reached, he said, appealing for food and water. Power was knocked out and there was no mobile phone signal, making communication possible only by radio.
Reports from the other four islands were still coming in, so far with dozens of fatalities.
The typhoon barrelled through six central Philippine islands, wiping away buildings and leveling seaside homes with ferocious winds of 147mph and gusts of 170mph. By those measurements, Haiyan would be comparable to a strong Category 4 hurricane in the US, and nearly in the top category, a 5.
It weakened today to 103mph with stronger gusts and is forecast to lose strength further when it hits northern Vietnam's Thanh Hoa province later.
In hardest-hit Tacloban, about 300-400 bodies have already been recovered but there are "still a lot under the debris" Mr Lim said. A mass burial is planned in Palo town near Tacloban.
Many corpses hung on tree branches, buildings and pavements. "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.
"They were covered with just anything - tarpaulin, roofing sheets, cardboards." Asked how many, she said: "Well over 100 where we passed."
Interior secretary Mar Roxas said a massive rescue operation was under way, saying: "We expect a very high number of fatalities as well as injured," after visiting Tacloban.
"All systems, all vestiges of modern living - communications, power, water - all are down. Media is down, so there is no way to communicate with the people in a mass sort of way."
President Benigno Aquino, who landed in Tacloban today for a first-hand look at the disaster, said the government's priority was to restore power and communications in isolated areas to allow the delivery of relief and medical assistance to victims.
The Philippines has no resources on its own to deal with a disaster of this magnitude, and the US and other governments and agencies are mounting a major relief effort, said Philippine Red Cross chairman Richard Gordon.
At the request of the Philippine government, US defence secretary Chuck Hagel directed America's Pacific Command to deploy ships and aircraft to support search and rescue operations and airlift emergency supplies.
European Commission president Jose Manuel Barroso, said in a message to Mr Aquino that the EC had sent a team to assist the Philippine authorities and "we stand ready to contribute with urgent relief and assistance if so required in this hour of need".
Even by the standards of the Philippines, which is buffeted by many natural calamities - about 20 typhoons a year, earthquakes and volcanic eruptions - the latest disaster shocked the impoverished nation of 96 million people.
If the typhoon death toll is confirmed, it would be the deadliest natural catastrophe on record in the Philippines. The deadliest typhoon before Haiyan was Tropical Storm Thelma in November 1991, which killed around 5,100 people in the central Philippines.
The deadliest disaster so far was the 1976 magnitude 7.9 earthquake that triggered a tsunami in the Moro Gulf in the southern Philippines, killing 5,791 people.
Tim Ticar, a tourism officer, said 6,000 foreigners and locals were stranded on the popular resort island of Boracay, one of the tourist spots in the typhoon's path.
United Nations secretary general Ban Ki-moon offered his condolences and said UN humanitarian agencies were working closely with the Philippine government to respond rapidly with emergency assistance.
Unicef estimated that about 1.7 million children were living in areas affected by the typhoon.. Unicef's supply division in Copenhagen was loading 60 tonnes of relief supplies for an emergency airlift expected to arrive in the Philippines on Tuesday.
In Vietnam, preparations for the typhoon were under way. About 600,000 people from the central region who had been evacuated returned home because the storm changed course and was instead heading for the northern coast, where authorities began evacuating nearly 100,000 in three northern provinces.