Tropical storm Washi raked across the southern Philippines, unleashing mammoth floods across vast areas that left almost 200 people dead and nearly 400 more missing, officials said Saturday.

They said 20,000 soldiers had been mobilised in a huge rescue and relief operation across the stricken north coast of the island of Mindanao, where the major ports of Cagayan de Oro and Iligan were worst hit.

Iligan mayor Lawrence Cruz described rampaging floodwaters from swollen rivers that swamped up to a quarter of the land area of the city of 100,000.

"It's the worst flood in the history of our city," Cruz told GMA television. "It happened so fast, at a time when people were fast asleep."

The station showed dramatic pictures of a family escaping out of the window of their home in the town as the floods rose, and rescue workers in orange vests shepherding survivors to safety above chest-deep waters.

Marlyn Manos, an Iligan resident, recounted how she and her children watched in terror from their rooftop as flash floods demolished neighbours' homes.

"All the small houses behind ours were destroyed, and many of my neighbours are missing," she said.

The region's military spokesmen said 97 bodies were recovered in Cagayan de Oro, with another 75 corpses found in Iligan.

Fifteen people who were swept out to sea were rescued off Iligan but another 250 remained unaccounted for in the town, they said, with 125 more missing in Cagayan de Oro, a city of half a million people.

Three people also drowned in the town of Polanco and five were killed in a landslide in mountains near the town of Monkayo, the National Disaster Risk Reduction and Management Council said in Manila.

After hitting the southern ports, Washi brushed past the central island of Negros, unleashing more floods that killed 18 people there, the council's executive director Benito Ramos told AFP.

The western island of Palawan is expected to be hit on Saturday night with peak winds of 75 miles (46.6 miles) after Washi crosses the Sulu Sea, the state weather service said.

Ramos suggested some Mindanao residents had underestimated the threat posed by the approaching storm, in a region which is outside the country's typhoon belt.

"Storms rarely hit this area and people probably became complacent even though they knew it was heading their way," Ramos said.

Eric Carillo, an Iligan resident, told GMA the rains started pouring heavily late Friday but his family, who emerged alive from the floods, were not unduly alarmed and did not seek higher ground.

"I've been around for 47 years and this was the worst flooding I have ever experienced," he added.

Iligan tourism officer Pat Noel told AFP waters began rising shortly before midnight (1600 GMT Friday) as people slept, sweeping houses made of light materials and their inhabitants along the riverbanks.

"Many of them told me they sought refuge on their rooftops," he said after joining the first wave of rescuers at daybreak.

Two of the three rivers that flow into the port of Iligan had overflowed, he added, and a popular radio commentator was among those killed.

Social Welfare Secretary Corazon Soliman said the flooding affected more than 22,000 families, but government officials could not give the total number of people who had lost their homes.

President Benigno Aquino has ordered 10 evacuation centres to be put up in the affected areas of Mindanao, his spokeswoman Abigail Valte said on government radio.

The Philippines is struck by about 20 major storms annually, with most hitting Luzon, the largest and most populous island in the Southeast Asian archipelago.