Packing maximum sustained wind speeds of 185 kilometres (115 miles) an hour, Man-yi slammed into Catanduanes island late Saturday, and the main island of Luzon on Sunday afternoon.

The sixth major storm to batter the Philippines in a month dumped heavy rain, smashed flimsy buildings, knocked out power and claimed at least eight lives.

The national weather service had warned of a "potentially catastrophic" impact from Man-yi, which was a super typhoon when it hit, but President Ferdinand Marcos said Monday it "wasn't as bad as we feared".

As people cleaned up on Monday, floods began hitting communities in the north after water from Magat Dam was released, causing the Cagayan river and some tributaries to overflow.

Rooftops could be seen poking through brown water in Ilagan city in Isabela province while buildings and roads near Tuguegarao city in Cagayan province were inundated.

"If Magat Dam continues to release water on all of its seven gates, Ilagan city might get erased from the map due to flooding," Jun Montereal, chairman of the city's disaster preparedness committee, told AFP, estimating 500 houses had been flooded.

"This is one of the gravest incidents that we have ever experienced because of the typhoon."

Carlo Ablan, who helps oversee operations at the dam, said water was released after a "huge volume" of inflows due to rain from Man-yi.

"If we won't be releasing water, the worst possible scenario will be our dam would collapse and that will be a much bigger problem," Ablan said.

- Heavy damage -

At least eight people were killed when typhoon Man-yi slammed into the islands over the weekend, including a 79-year-old man, who died in Camarines Norte after his motorbike was caught in a power line, police said.

Seven people died and three were injured when a landslide buried their house in Nueva Vizcaya province in Luzon, Kristine Falcon of the provincial disaster agency told AFP

Power outages across the island province of Catanduanes could last for months after Man-yi toppled electricity poles, provincial information officer Camille Gianan told AFP.

"Catanduanes has been heavily damaged by that typhoon -- we need food packs, hygiene kits and construction materials," Gianan said.

"Most houses with light materials were flattened while some houses made of concrete had their roofs, doors and windows destroyed."

In the coastal town of Baler in Aurora province, clean-up operations were underway to remove felled trees and debris blocking roads and waterways.

"Most of the houses here are made of light materials so even now, before the inspection, we are expecting heavy damage on many houses in town," disaster officer Neil Rojo told AFP.

"We've also received reports of roofs that went flying with the wind last night... it was the fierce wind that got us scared, not exactly the heavy rains."

- Storm weakens -

Man-yi weakened significantly as it traversed the mountains of Luzon and was downgraded to a severe tropical storm as it swept over the South China Sea towards Vietnam on Monday.

More than a million people in the Philippines fled their homes ahead of the storm, which followed an unusual streak of violent weather.

Climate change is increasing the intensity of storms, leading to heavier rains, flash floods and stronger gusts.

At least 171 people in the Philippines died in the past month's storms, which left thousands homeless and wiped out crops and livestock.

US Defense Secretary Lloyd Austin, in Manila for talks with his Philippine counterpart and President Marcos, announced Monday an additional $1 million in humanitarian aid to victims of the recent storms.

About 20 big storms and typhoons hit the Southeast Asian nation or its surrounding waters each year, killing scores of people, but it is rare for multiple such weather events to take place in a small window.

This month, four storms were clustered simultaneously in the Pacific basin, which the Japan Meteorological Agency told AFP was the first time such an occurrence had been observed in November since its records began in 1951.