Super Typhoon Megi slammed ashore along the Philippines' north-eastern coast today with ferocious winds of 140mph - the strongest cyclone to hit the country in years.
Thousands sought shelter while authorities warned millions of residents and rice farmers along the typhoon's path to look out for damage to crops, homes and power lines.
Weather forecaster Robert Sawi said the eye of the typhoon made landfall at midday local time at Palanan Bay in Isabela province.
As it crossed the main northern island of Luzon, Mr Sawi warned of possible floods and landslides, particularly in the Cordillera mountains.
Flood-ravaged areas of China and Vietnam also were bracing for more rains from the powerful storm.
Megi was expected to move on towards southern China, which has already evacuated more than 100,000 people from villages because of earlier flooding, according to the China Meteorological Administration.
With its ferocious wind and heavy rainfall, Megi has become the most powerful typhoon to hit the Philippines in four years, government forecasters say. A 2006 howler with 155mph winds set off mudslides that buried entire villages, killing about 1,000 people.
Philippine weather officials issued the highest of a four-tier public storm alert for the two coastal provinces of Isabela and Cagayan and three mountain provinces where the typhoon is expected to pass before exiting the main northern island of Luzon into the South China Sea.
More than 3,000 people in coastal areas moved to school buildings and town halls that were turned into evacuation centres. Classes and outdoor activities were cancelled and officials advised families to have one person stay awake overnight for any contingency.
Ships and fishing vessels were told to stay in ports, and several domestic flights were cancelled.
Thousands of military reserve officers and volunteers were on standby, along with helicopters, including six Chinooks that were committed by US troops holding war exercises with Filipino soldiers near Manila, said Benito Ramos, a top disaster-response official.
Rescue boats and thousands of food packs have been pre-positioned near vulnerable areas, he said.
"This is like preparing for war," Mr Ramos, a retired army general, said. "We know the past lessons and we're aiming for zero casualties."
An angry President Benigno Aquino sacked the head of the weather bureau in July for failing to predict that a typhoon would hit Manila. That storm killed more than 100 people in Manila and outlying provinces.
Weather forecasts said the capital was expected to be spared a direct hit this time although the lowest weather alert was in effect today with pre-schools closed.
In Cagayan, a vast agricultural valley criss-crossed by rivers and creeks, authorities ordered villagers to move out of high-risk neighbourhoods in 12 coastal towns.
"If nobody will budge, we may carry out forced evacuations," said Bonifacio Cuarteros of the provincial disaster office.
Farmers in Cagayan, a rice- and tobacco-producing region of more than a million people about 250 miles north east of Manila, have been warned to harvest as much of their crops as possible before the typhoon hits or risk losses.
With its current course and speed, the typhoon is expected to barrel across the northern tip of Luzon then blow into the South China Sea later today towards northern Vietnam or southern China.
China's National Meteorological Centre issued its second-highest alert for potential "wild winds and huge waves", warning vessels to take shelter and urging authorities to brace for emergencies, the state-run Xinhua News Agency said.
Floods triggered by heavy rains forced more than 100,000 people to evacuate in China's southern island province of Hainan, where heavy rains have already left thousands homeless over the weekend, Xinhua said. More rain is expected as Typhoon Megi approaches the region.
Record-level flooding in Hainan over the past month has damaged roads, overflowed reservoirs and cut off telecommunication networks across the region.
One man trying to rescue his water buffalo slipped and fell into a river and probably drowned, said Bonifacio Cuarteros, an official with the Cagayan provincial disaster agency.
As it crashed ashore, the typhoon whipped up huge waves and toppled electricity poles, cutting off power, phone and internet services in many areas.
There was zero visibility and radio reports said the wind was so powerful that people could not take more than a step at a time.