The storm will likely go down in history as the most powerful typhoon in recorded history to make landfall.
The world's strongest recorded hurricane, typhoon or cyclone to previously make landfall was Hurricane Camille of 1969, which roared ashore with 190 mph winds in Mississippi. Haiyan's sustained winds easily make it a category 5 hurricane.
Television images from Tacloban city on Leyte Island showed a street under knee-deep floodwater carrying debris that had been blown down by the fierce winds. Tin roofing sheets ripped from buildings were flying above the street.
Although Typhoon Haiyan (HIGH-y-an) has diminished to a category 2 storm, it is expected to cause extensive damage when it hits Vietnam on Sunday according to Dr. Jeff Masters of Weather Underground told ABC News Radio. He says the country is not equipped for the type of rain and wind expected.
"The buildings in Vietnam aren't to the same sort of codes we have here in the U.S. and they're not going to be able to withstand 50, 70, 90 mile per hour winds near the coast," said Masters.
Haiyan is expected to move over South China Sea and into Vietnam by Sunday by about 5 p.m. Eastern Time with strong winds up to 105 mph. The storm is forecast to significantly weaken as it reaches Laos and inland China, but tropical rain could produce deadly flash floods.
Haiyan is about 300 miles wide, roughly the distance from Boston to Philadelphia. The storm surge could likely exceed 23 feet, compared with the 14 feet Superstorm Sandy brought with it last year when it hit the East Coast of the U.S.
"It's stronger in an absolute sense than Sandy but the strongest winds are concentrated very close to the center as compared to a storm like Sandy where the strong winds extended very far away from the center," the National Hurricane Center's Richard Pass told ABC News Radio.
Haiyan marks the 24th named storm this year to hit the vulnerable islands.
ABC News Radio, Anthony Castellano and Alexis Shaw contributed to this report.