The Philippine Red Cross says a super typhoon that plowed through the central Philippines on Friday may have killed more than 1,200 people.
The official death toll released by the Philippine government on Saturday was 138, but President Benigno Aquino said he believes "there will be substantially more casualties."
Philippine Red Cross secretary general Gwendolyn Pang said her organization estimates that at least 1,000 people were killed on Leyte island with another 200 killed on nearby Samar island.
Super Typhoon Haiyan, known locally as Yolanda, slammed into the islands early Friday. It had maximum sustained winds of around 300 kilometers an hour and sent waves up to five meters high crashing through island communities.
Haiyan was one of the most powerful cyclones on record to make landfall anywhere in the world.
A United Nations Disaster Assessment Coordination Team that flew into Leyte's capital of Tacloban said it found "scenes of total devastation." It said roads from the airport to the city of 200,000 people were impassable, leaving helicopters as the only means of travel.
The World Food Program was providing emergency assistance to government agencies that are helping victims.
The U.N. team leader Sebastian Rhodes Stampa said the last time he saw destruction on such a scale was in the aftermath of the December 2004 Indian Ocean Tsunami.
Philippine Interior Secretary Mar Roxas also arrived in Tacloban on Saturday and said the devastation was "really horrific ... a great human tragedy." The government helped to evacuate people in the region in the days before the storm, but it appeared that many stayed in their homes.
Some Tacloban residents wept as they recounted losing loved ones. Others appeared dazed. Bodies lay in the streets, covered in sheets and bags. People also began looting stores, looking for food to survive or carrying away household appliances.
Roxas said the Philippine government has deployed security forces to the area to conduct rescue operations, and to try to restore electricity and water.
U.S. Secretary of State John Kerry issued a statement saying Washington is "ready to help" the Philippines, a longtime regional ally, as it deals with Haiyan's aftermath.
Typhoon Haiyan weakened after crossing the Philippines but regained some strength as it moved westward over the South China Sea toward Vietnam.
The storm took a northwesterly turn on Saturday, and weather agencies predicted it would come ashore in northern Vietnam on Monday morning local time, just south of the capital, Hanoi. Earlier, it appeared that Haiyan would hit Vietnam's central provinces.
Vietnamese authorities carried out mass evacuations in at least four coastal provinces on Saturday, sending hundreds of thousands of people to shelters.
Haiyan's new projected path also put the southern Chinese island of Hainan at risk of strong winds and heavy rain. The Chinese government issued an alert to local authorities to prepare for flooding and called fishing boats back to port.