The death toll has risen significantly in the past day. Officials say 800 more people are still missing on Mindanao, mostly in the worst-hit coastal cities of Cagayan de Oro and Iligan, where some people were swept out to sea.
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Many of the victims were asleep when the storm hit, said Benito Ramos, head of the national disaster rescue agency.
Rivers burst their banks after 25 millimeters of rain fell within a period of 24 hours, while the island was battered by winds of up to 55 miles per hour, the BBC said.
Iligan mayor Lawrence Cruz said a quarter the city was swamped by floods, along with at least 10 villages on the outskirts of Iligan.
Cruz told GMA television:
"It's the worst flood in the history of our city. It happened so fast, at a time when people were fast asleep."
Military spokesman Lt. Col. Randolph Cabangbang said about 250 people were unaccounted for in Iligan, the Associated Press reported.
Meanwhile Cagayan de Oro city councilor Alvin Bacal said 107 people had died there, with an entire army division of some 10,000 soldiers mounting a rescue effort.
State weather forecasters said Tropical Storm Washi, which is called "Sendong" in the Philippines, made landfall on the western island of Palawan late Saturday.