* Typhoon barrelling out of the Philippines, heading for Vietnam
* At least 100 dead, 100 injured
* "We thought it was a tsunami," says survivor
(Adds Vietnam preparations, airport destroyed, other details throughout)
TACLOBAN, Philippines, Nov 9 (Reuters) - Possibly the strongest typhoon ever to hit land devastated the central Philippine city of Tacloban, killing at least 100 people, turning houses into rubble and levelling the airport in a surge of flood water and high wind, officials said on Saturday.
The toll of death and damage from Typhoon Haiyan on Friday is expected to rise sharply as rescue workers and soldiers reach areas cut off by the massive, fast-moving storm, now barrelling out of the Philippines towards Vietnam.
The category 5 "super typhoon" weakened to a category 4 on Saturday, though forecasters said it could strengthen again over the South China Sea on its course to hit Vietnam early on Sunday.
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 resume communications with officials in Tacloban, a city of about 220,000 that appeared to suffer the worst of the typhoon, but a government official estimated at least 100 were killed and 100 wounded.
"Bodies are lying on the street," said Captain John Andrews, deputy director general of the Civil Aviation Authority.
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, suggesting the toll could be higher.
Television images showed residents of Tacloban, about 580 km (360 miles) southeast of Manila, wading through flooded streets that were littered half-submerged cars.
Before communications were cut on Friday, city officials had reported heavy flooding. Mobile phone networks and most roads were cut off.
"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.
The city's airport, which is close to the coast, was destroyed by huge waves and several soldiers based there were missing, a military officer told Reuters.
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.
"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 two 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, 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 709 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 Stuart Grudgings and Nick Macfie)