* Typhoon crossing South China Sea, heading for Vietnam
* At least 100 dead, 100 injured
* "We thought it was a tsunami," says survivor
(Adds comments, details)
TACLOBAN, Philippines, Nov 9 (Reuters) - One of the strongest typhoons ever to make landfall churned through the Philippine archipelago in a straight line from east to west and devastated central provinces, killing at least 100 people in a surge of flood water, officials said on Saturday.
The death toll from Typhoon Haiyan is expected to rise sharply as rescue workers reach areas cut off by the fast-moving storm, whose circumference eclipsed the whole country and which late on Saturday was heading for Vietnam.
Roads in the coastal city of Tacloban in the central Leyte province, one of the worst-hit areas, were either under water or blocked by fallen trees and power lines and debris from homes blown away by Haiyan.
Bodies covered in plastic were lying on the streets.
"The last time I saw something of this scale was in the aftermath of the Indian Ocean Tsunami," said Sebastian Rhodes Stampa, head of the U.N. Disaster Assessment Coordination Team sent to Tacloban.
"This is destruction on a massive scale. There are cars thrown like tumbleweed and the streets are strewn with debris."
The category 5 "super typhoon" weakened to a category 4 on Saturday, though forecasters said it could strengthen again over the South China Sea en route to Vietnam.
Authorities in 15 provinces in Vietnam have started to call back boats and prepare for possible landslides. Nearly 300,000 people were moved to safer areas in two provinces alone - Da Nang and Quang Nam - according to the government's website.
The Philippines has yet to restore communications with officials in Tacloban, a city of about 220,000, but a government official estimated at least 100 were killed and more than 100 wounded.
The national disaster agency has yet to confirm the toll but broken power poles, trees, bent tin roofs and splintered houses littered the streets of the city about 580 km (360 miles) southeast of Manila. The airport was destroyed as raging seawaters swept through the city.
"Almost all houses were destroyed, many are totally damaged. Only a few are left standing," said Major Rey Balido, a spokesman for the national disaster agency.
Local television network ABS-CBN showed images of looting in one of the city's biggest malls, with residents carting away everything from appliances to suitcases and grocery items.
About a million people took shelter in 37 provinces after President Benigno Aquino appealed to those in the typhoon's path to leave vulnerable areas.
"For casualties, we think it will be substantially more," Aquino told reporters.
"WE THOUGHT IT WAS A TSUNAMI"
Officials started evacuating residents from low-lying areas, coastlines and hilly villages as early as three days before the typhoon struck on Friday, helping to limit the loss of life, several officials said. But not all headed the call to evacuate.
"I saw those big waves and immediately told my neighbours to flee. We thought it was a tsunami," said Floremil Mazo, a villager in southeastern Davao Oriental province.
Meteorologists said the impact may not have been as strong as feared because the storm was moving so quickly, reducing the risk of flooding and landslides from torrential rain, the biggest causes of typhoon casualties in the Philippines.
Ferry services and airports in the central Philippines remained closed, hampering aid deliveries to Tacloban, although the military said three C-130 transport planes managed to land at its airport on Saturday.
At least two people were killed on the tourist destination island of Cebu, three in Iloilo province and another three in Coron town in southwestern Palawan province, radio reports said.
"I never thought the winds would be that strong that they could destroy my house," LynLyn Golfan of Cebu said in a television interview while sifting through the debris.
By Saturday afternoon, the typhoon was hovering 765 km west of San Jose in southwestern Occidental Mindoro province, packing winds of a maximum 185 kph, with gusts of up to 220 kph.
The storm lashed the islands of Leyte and Samar with 275-kph wind gusts and 5-6 metre (15-19 ft) waves on Friday before scouring the northern tip of Cebu province. It weakened slightly as it moved west-northwest near the tourist island of Boracay, later hitting Mindoro island.
Haiyan was the second category 5 typhoon to hit the Philippines this year after Typhoon Usagi in September. An average of 20 typhoons strike every year, and Haiyan was the 24th so far this year.
Last year, Typhoon Bopha flattened three towns in southern Mindanao, killing 1,100 people and causing damage of more than $1 billion.
(Additional reporting by Rosemarie Francisco, Manuel Mogato and Karen Lema in Manila and Nguyen Phuong Linh in Hanoi; Editing by Nick Macfie)