The world's most powerful typhoon this year gained strength on Thursday as it swirled towards the Philippines, forcing mass evacuations across a vast swathe of the disaster-weary nation.
Authorities warned more than 12 million people were at risk from Typhoon Haiyan, which was generating wind gusts exceeding 330 kilometres (200 miles) an hour and set to hit on Friday morning.
"This is a very dangerous typhoon, local officials know where the vulnerable areas are and have given instructions on evacuations," state weather forecaster Glaiza Escullar told AFP.
"There are not too many mountains on its path to deflect the force of impact, making it more dangerous."
Haiyan was expected make landfall on Samar island, about 600 kilometres southeast of Manila, then cut across the central and southern Philippines before exiting into the South China Sea late on Saturday.
Escullar said Haiyan, which was advancing with a giant, 600-kilometre front, was expected to hit areas still recovering from a devastating 2011 storm and a 7.1-magnitude quake last month.
They include the central island of Bohol, the epicentre of the earthquake that killed 222 people, where at least 5,000 survivors are still living in tents while waiting for new homes.
"The provincial governor has ordered local disaster officials to ensure that pre-emptive evacuations are done, both for those living in tents as well as those in flood-prone areas," Bohol provincial administrator Alfonso Damalerio told AFP.
Other vulnerable areas were the port cities of Cagayan de Oro and Iligan on the southern island of Mindanao, where flash floods induced by Tropical Storm Washi killed more than 1,000 people in December 2011.
Authorities said evacuations were taking place in many other towns and villages in Haiyan's path, while schools were closed, ferry services suspended and fishermen ordered to secure their vessels.
Cebu Pacific said it had cancelled 110 domestic flights and four international ones between Thursday and Saturday because of the storm.
Haiyan had maximum sustained winds on Thursday afternoon of 278 kilometres an hour, and gusts of 333 kilometres an hour, according to the US Navy's Joint Typhoon Warning Centre.
This would make it the world's strongest typhoon this year, according to David Michael Padua, a meteorologist with the Weather Philippines Foundation, a storm monitoring organisation that runs the www.weather.com.ph website.
The Philippines is battered by an average of 20 major storms or typhoons each year, many of them deadly, but scientists have said climate change may be increasing their ferocity and frequency.
The Philippines endured the world's strongest storm of 2012, when Typhoon Bopha left about 2,000 people dead or missing on Mindanao island in December.
The Global Disaster Alert and Coordination System, jointly run by the United Nations and the European Commission, said nearly 16 million people, including more than 12 million from the Philippines, were at risk from Haiyan.
The others were in Laos and Vietnam, which are forecast to be hit on Sunday, it said on its website.
"Haiyan can have a high humanitarian impact," it said.