The Philippines raised its highest storm alert and evacuated thousands of people on Thursday, as Super Typhoon Usagi barrelled towards its already disaster-ravaged north.

Packing sustained winds of up to 185 kilometres an hour, Usagi is set to hit the main island of Luzon later on Thurday -- the fifth storm to threaten the country in just three weeks.

The brutal wave of weather disturbances has already killed 159 people and prompted the United Nations to request US$32.9 million in aid for the worst-affected regions.

The national weather agency said the winds could cause "almost total damage to structures of light materials, especially in highly exposed coastal areas", and "heavy damage" to buildings otherwise considered "low-risk".

"Intense to torrential rain" and potentially "life-threatening" coastal waves of up to three metres were also forecast over two days, with the storm warning raised to the highest signal on a five-step scale.

In Cagayan province, where the storm is expected to make landfall, officials worked in driving rain to remove residents along the coasts and on the banks of already swollen rivers.

"Yesterday it was preemptive evacuations. Now we're doing forced evacuations," local disaster official Edward Gaspar said, adding 1,404 residents were sheltering at a municipal gym.

"There are many more evacuees in nearby villages but we haven't had time to visit and count them," he added.

Cagayan's civil defence chief Rueli Rapsing said he expects local governments to take 40,000 people to shelters, roughly the same number that were preemptively evacuated ahead of Typhoon Yinxing, which struck Cagayan's north coast earlier this month.

More than 5,000 Cagayan residents were still in shelters following the previous storms because the Cagayan River, the country's largest, remained swollen from heavy rain that fell in several provinces upstream.

After Usagi, Tropical Storm Man-yi is also forecast to strike the Philippines' population heartland around the capital Manila this weekend.

"Typhoons are overlapping. As soon as communities attempt to recover from the shock, the next tropical storm is already hitting them again," UN Philippines Resident and Humanitarian Coordinator Gustavo Gonzalez said.

"In this context, the response capacity gets exhausted and budgets depleted."

About 20 big storms and typhoons hit the archipelago nation or its surrounding waters each year, killing scores of people and keeping millions in enduring poverty.

A recent study showed that storms in the Asia-Pacific region are increasingly forming closer to coastlines, intensifying more rapidly and lasting longer over land due to climate change. (AFP)