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One of the most intense typhoons ever recorded has torn into the Philippines, triggering flash floods and ripping down buildings as millions of people huddle indoors.
The strength of the wind made it one of the four most powerful typhoons ever recorded in the world, and the most powerful to have made landfall, according to Jeff Masters, the director of meteorology at US-based Weather Underground.
Masters said he expected the damage in Guiuan, the fishing town of about 40,000 people that was the first to be hit after Haiyan swept in from the Pacific Ocean, to be "catastrophic".
"Perhaps the greatest wind damage any city on Earth has endured from a tropical cyclone in the past century," Masters wrote on his blog for the weather monitoring website.
Communication with Guiuan was cut off immediately after Haiyan hit, and the civil defence office says it's too early to give an assessment of the damage there.
But in Tacloban, a nearby city of more than 200,000 people, streets are flooded and some buildings have been torn down, according to footage broadcast on ABS CBN television.
Twitter users have begun posting photos of the damage.
Haiyan had maximum sustained winds on Friday morning of 315km/h, and gusts of 379km/h, according to the US Navy's Joint Typhoon Warning Centre.
Masters said the previous record for the strongest typhoon to make landfall was Hurricane Camille, which hit Mississippi in the United States with winds of 305km/h in 1969.
Philippine President Benigno Aquino on Thursday warned his countrymen to make all possible preparations for Haiyan.
"To our local officials, your constituents are facing a serious peril. Let us do all we can while (Haiyan) has not yet hit land," Aquino said in a nationally televised address.
Aquino warned areas within the 600km typhoon front would be exposed to severe flooding as well as devastating winds, while coastal areas may see waves six metres high.
More than 125,000 people in the most vulnerable areas had been moved to evacuation centres before Haiyan hit, according to the civil defence office, and millions of others braced for the typhoon in their homes.
Authorities said schools in the storm's path were closed, ferry services suspended and fishermen ordered to secure their vessels.
In the capital of Manila, which was on the northern edge of the typhoon's path, many schools were closed amid forecasts of heavy rain.
Philippine Airlines, Cebu Pacific and other carriers announced the suspension of hundreds of flights, mostly domestic but also some international.