Residents of Tacloban told terrifying accounts of being swept away by a wall of water. Jean Mae Amande, 22, said she was washed several miles from her home by the surge of water. The current ripped her out to sea before pushing her back to shore where she was able to cling to a tree and grab a rope thrown from a boat.
"It's a miracle that the ship was there," Amande said.
Nearly 620,000 people were displaced and 9.5 million "affected" across the Philippines, the U.N.'s Office for the Coordination of Humanitarian Affairs said in a statement.
(Watch this: Philippines Red Cross: Typhoon is 'overwhelming')
"The situation is bad, the devastation has been significant. In some cases the devastation has been total," Secretary to the Cabinet Rene Almendras told reporters.
Mobs attacked trucks loaded with food, tents and water on Tanauan bridge in Leyte, Philippines Red Cross chairman Richard Gordon saud.
Dozens of residents clamored for help at the airport gates in Tacloban.
"Help us, help us. Where is President [Benigno] Aquino? We need water, we are very thirsty," one woman shouted. "When are you going to get bodies from the streets?"
Maria Elnos, a nurse at Tacloban's one main hospital, was among hundreds pleading unsuccessfully to get on a military C-130 plane late Sunday.
"I lost my house, I lost everything," she told Reuters. " I want to get out. My food supply will run out in two days."
Aid workers and officials worried that smaller communities outside Tacloban had fared even worse.
"While many communities are very difficult to reach, with roads, airports and bridges destroyed or blocked with debris, agencies have begun airlifting food, health, shelter, medical and other life-saving supplies and have deployed specialist teams and vital logistics support," United Nations Secretary General Ban Ki-moon said in a statement.
A World Vision official said early reports suggested that as much as 90 percent of northern Cebu had been destroyed. An aid team from Oxfam reported "utter destruction" in the northern-most tip of Cebu, the charity said.
Weather forecasters said they believed this was the strongest storm ever to hit land.
"After researching this, we believe that when it hit the Philippines this may have been the strongest ever recorded to storm to make landfall," said Kevin North, a lead meteorologist at the Weather Channel. "There have been more powerful storms over the sea, but this could be the strongest ever to hit land."
More bad weather was on the way with a depression due to bring rain to the central and southern Philippines on Tuesday, the weather bureau said.
On Sunday, American officials dispatched a team of some 90 Marines and sailors—the first wave of U.S. military help—flew to the Philippines to assist with search and rescue operations and provide air support.
U.S. Pacific Command had authorized the US Marines to bring in transportation, including C130 cargo planes.
"Not just military but USAID (US Agency for International Development) is here, international relief organisations are here," said Brig. Gen. Paul Kennedy, deputy commanding general of III Marine Expeditionary Force.
"Obviously the military has logistics capabilities that are unique. So the United States Pacific Command has authorized Marine Forces Pacific to bring in transportation. We have C-130s coming in," he said.
(Read more: Philippine IPO in the eye of the storm)
USAID is also sending emergency shelter and hygiene materials expected to arrive early this week. It is sending 55 tons of emergency food to feed 20,000 children and 15,000 adults for up to five days. The U.S. Embassy is sending $100,000 for water and sanitation support.
—By Nancy Snyderman, Harry Smith and F. Brinley Bruton for NBC News, with reports from Reuters and the Associated Press