Sustained winds of more than 100mph have caused landslides, ripped off roofs and brought down trees in the Philippines as Typhoon Mangkhut pummeled northern areas of the country.
Two women died after a hillside collapsed in the city of Baguio, police said.
A woman also died in neighbouring Taiwan after being swept out to sea.
The storm, with gusts reaching 160mph, knocked out power as it tore across the northern part of Luzon island - an area which is home to around 10 million people, many of whom live in flimsy wooden homes.
Thousands of evacuees have taken refuge in emergency shelters.
There are storm warnings in 10 northern provinces.
"We believe there has been a lot of damage," social welfare secretary Virginia Orogo said.
Defence Secretary Delfin Lorenzana said officials were verifying whether two children had drowned in northeastern Cagayan province.
"It's still a life and death situation," he said.
Mr Lorenzana added that Tuguegarao airport's terminal roof and windows had been shattered, with the wind flipping chairs and tables around inside.
It is the start of the rice and corn harvesting season in Cagayan province, where farmers have been scrambling to save what they can of their crops.
The Philippines is no stranger to severe weather, where they are an average of 20 typhoons and storms each year.
Mangkhut is heading towards Hong Kong, where Security Minister John Lee Ka-chiu warned residents it would be bringing "winds and rains of extraordinary speeds, scope and severity".
He added: "Each department must have a sense of crisis, make a comprehensive assessment and plan, and prepare for the worst."
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