Local officials say the death toll in a central province that took the brunt of Typhoon Haiyan could reach as high as 10,000.
Police and provincial officials provided the estimate on Sunday after assessing damage in Leyte province, where they say the destruction was overwhelming. The regional police chief said most of the deaths resulted from drowning and collapsed buildings
Philippine Interior Secretary Mar Roxas says it is difficult to describe the extent of damage in Leyte's capital, Tacloban.
"The devastation is - I do not have the words for it. It is really horrific. It is a great human tragedy. There is no power. There is no light."
The Associated Press says Tacloban's city administrator told reporters as many as 400 bodies have been recovered.
The typhoon roared into the Philippines as one of the most powerful storms on record, with maximum sustained winds of about 300 kilometers an hour.
It is now in open water, churning towards Vietnam, where forecasters expect it to make landfall late Sunday or Monday.
Vietnamese authorities have evacuated several hundred thousand people from coastal areas, where the storm's outer bands are already causing high winds and rough seas.
U.N. emergency relief coordinator Valerie Amos said a U.N. disaster and assessment team has been deployed to Tacloban.
Separately, U.N. Secretary General Ban Ki-moon offered his condolences to the Philippines, saying he was deeply saddened by the "extensive loss of life."
The U.S. is assisting with relief efforts. In a Saturday statement, the Defense Department said the U.S. Pacific Command had been directed to assist in search and rescue operations and aircraft support.
Also, a U.S. relief team has been deployed to the region. The U.S. Agency for International Development says the team will conduct damage assessments, track conditions and "advise on additional needs."
Typhoon Haiyan weakened after crossing the Philippines but regained some strength as it began moving westward in the South China Sea .