Super Typhoon Haiyan, one of the strongest tropical cyclones ever observed, made landfall Friday morning in the Philippines, the country's weather service reported.
Thousands of people in vulnerable areas of the central Philippines were evacuated as the monster storm spun toward the country.
With sustained winds of 315 kph (195 mph) and gusts as strong as 380 kph (235 mph), Haiyan churned across the Western Pacific into the Philippines.
Its wind strength makes it equivalent to an exceptionally strong Category 5 hurricane.
Haiyan will move over the many islands of the central Philippines over the next 18 hours before exiting into the South China Sea overnight Friday into Saturday. Haiyan will weaken slightly as the storm crosses land, but forecasters with the Philippine weather agency, Pagasa, predict that it will maintain super typhoon intensity throughout its passage of the islands.
The storm, known as Yolanda in the Philippines, is so large in diameter that clouds from it are affecting two-thirds of the country, which extends over 1,850 kilometers (1,150 miles).
Authorities in the region had moved more than 3,800 people to evacuation centers by late Thursday, Maj. Reynaldo Balido of the Philippine Office of Civil Defense said.
Most of those relocated live in Tacloban City, which sits on the coast of the island of Leyte and has a population of more than 200,000.
In a speech Thursday, President Benigno S. Aquino III warned residents of the "calamity our countrymen will face in these coming days."
"Let me repeat myself: This is a very real danger, and we can mitigate and lessen its effects if we use the information available to prepare," he said.
The government has three C-130 cargo aircraft ready to respond, as well as 32 planes and helicopters from the air force, the president said.
Officials have placed relief supplies in the areas that are expected to get hit, Aquino said.
"The effects of this storm can be eased through solidarity," he said.
Earthquake survivors vulnerable
As it moves across heavily populated areas of the central Philippines, Haiyan's high winds and torrential rain are expected to affect more than 25 million people. The storm system had a diameter of about 800 kilometers (500 miles) as of Friday.
Pagasa warned more than 30 provinces across the country Thursday to be prepared for possible flash floods and landslides.
Schools in many areas canceled classes, emergency services were put on high alert, and airlines canceled flights.
Some of the most vulnerable people are those living in makeshift shelters on the central Philippine island of Bohol.
Last month, a 7.1-magnitude earthquake hit the island, which lies close to the typhoon's predicted path. The quake killed at least 222 people, injured nearly 1,000 and displaced about 350,000, according to authorities.
Beach resort threatened
Another island in the storm's likely trajectory is the popular beach resort of Boracay. Some tourists there were cutting their vacations short to get away from the possible danger.
Ross Evans, an aviation professional from Florida, said there was "a definite urgency and panic" among the long lines of holidaymakers waiting for boats to get off Boracay on Thursday.
Speaking by phone before his flight to Manila took off, he said he felt "horrible" for those who may end up stuck in the storm's path.
Evans said he and his travel companions, who are leaving the Philippines two days earlier than planned, "feel very fortunate to have the ability to make arrangements to be safe."
Situated near an area of the Pacific Ocean where tropical cyclones form, the Philippines regularly suffers severe storm damage.
An average of 20 typhoons hit the archipelagic nation every year, and several of those cause serious damage.
In December, Typhoon Bopha wreaked widespread devastation on the southern Philippine island of Mindanao. The storm, the most powerful to hit the country that year, is estimated to have killed as many as 1,900 people.