Typhoon Nari pummelled the northern Philippines early Saturday, ripping roofs off buildings, killing 12 people and leaving more than two million without power.

Nari slammed into the country's east coast around midnight (1600 GMT Friday), toppling trees and pylons as it cut a westward swathe through the farming regions of the main island of Luzon, officials said.

"While there were relatively few casualties, a lot of areas are still flooded," Eduardo del Rosario, head of the National Disaster Risk Reduction and Management Council told a news conference.

Witnesses in the coastal town of Baler, near where Nari made landfall, said many large trees had been felled and clean-up crews with chainsaws were clearing the roads.

Government clerk Glenn Diwa, 34, said she and her husband spent a sleepless as the typhoon roared through the town of Capas, 90 kilometres (55 miles) north of Manila.

"It started close to midnight and lasted three hours. The wind was very strong and there was a whistling sound. After a while we heard torn roofing sheets clattering across the yard," she told AFP.

As Nari moved inland, dumping rain, a wall of mud fell on a police barracks near the town of Magalang, killing an officer awaiting deployment to rescue typhoon victims, the civil defence office in the region said.

Elsewhere in central Luzon, an old woman and four minors were crushed to death when trees crashed onto two houses and a vehicle, while the wall of a school collapsed and crushed an old man to death.

Another man was electrocuted by a loose power line while yet another died of a heart attack in an incident that disaster officials also blamed on Nari.

Two children and an elderly person drowned in the province of Bulacan, which suffered widespread flooding, provincial governor Wilhelmino Alvarado told ABS-CBN television in an interview.

The network aired footage of earth-coloured floodwaters climbing above river defences and swamping farmland.

Soldiers, police, and local government workers used military trucks to rescue residents in flooded communities across the towns of San Miguel and Minalin, the regional civil defence office there said.

"The wind picked up very quickly, very dramatically. We had the wind coming right off the ocean for four hours," said one witness on the east coast.

Even as Nari blew out to the South China Sea Saturday, with peak winds of 120 kilometres (75 miles) an hour according to the state weather service, the danger had not passed.

A farmer and a woman on separate motorbikes were nearly swept away and had to be pulled back to safety by policemen when they tried to cross a street that had turned into a raging river.

Farmer Frankie Gracia, 30 said he had been forced to butcher one of his pigs after it fell ill from exposure to the rain and wanted to cross the streaming floodwaters to take some of the pork to his relatives.

"I needed to reach the other side soon, otherwise the meat would spoil," he said.

The typhoon blacked out 37 towns and cities across the region.

Road and utility crews were out clearing roads and restoring power, but it could take up to two days before electricity is restored and major highways are reopened to traffic, Nigel Lontoc, a disaster official for the region, told AFP by telephone.

A total of 2.1 million people live in the areas now without electricity.

Four people were listed as missing, including a fisherman on the country's east coast who had been sleeping in his boat that was swept out to sea.

Three other fishermen who put to sea elsewhere before the typhoon have also failed to return, officials said.

About 3,000 people moved into government-run shelters amid warnings their communities could be hit by flooding and landslides, Lontoc said.

The typhoon spared the capital Manila, where the state weather service had warned on Friday about possible widespread flooding.

Projections from the Hong Kong Observatory had the storm gathering pace over the coming days as it heads towards the northeast coast of Vietnam.

The Philippines is hit by about 20 major storms or typhoons each year that occur mainly between June and October.