Jon Donnison reports from Manila: ''There are reports of 100 bodies lying in the streets of Tacloban''
At least 100 people have reportedly been killed by Typhoon Haiyan in one city, according to a Philippine official.
Capt John Andrews, deputy director general of the Civil Aviation Authority, said the bodies were lying in the streets of the city of Tacloban.
The storm ripped apart buildings and triggered landslides when it hit the central Philippines on Friday.
Power and communication lines were also cut to some areas.
Video from the city of Tacloban showed the city engulfed by water when the typhoon struck, the BBC's Jon Donnison reports from Manila.
Aid agencies are struggling to reach the city, as its airport has been badly damaged and only military flights are able to operate, he adds.
The Philippine government has praised the evacuation effort which at least until now seems to have kept the number of people killed relatively low.
But it may be days before the final death toll is known, our correspondent says.
Officials had said more than 12 million people were at risk. Much of the region affected had already been struggling to recover from an earthquake last month.
"We expect the level of destruction caused by Typhoon Haiyan to be extensive and devastating, and sadly we fear that many lives will be lost," said Save the Children's Philippines director Anna Lindenfors on Friday.
The typhoon is now heading for Vietnam, and is expected to make landfall on Sunday.
Vietnamese authorities have begun the mass evacuation of more than 100,000 people.
State media in Vietnam report that schools are being closed and people living in low lying coastal areas are being moved to temporary typhoon shelters on higher ground. Shipping has also been ordered back to port.
The storm made landfall on the Philippines shortly before dawn on Friday, bringing gusts that reached 379 km/h (235 mph), with waves as high as 15m (45ft), bringing up to 400mm (15.75 inches) of rain in places.
Meteorologists had earlier warned that the storm could be as devastating as Typhoon Bopha in 2012, which ravaged parts of the southern Philippines and left at least 1,000 people dead.
Schools and offices were closed, while ferry services and local flights were suspended. Hospitals and soldiers were on stand-by for rescue and relief operations.
Haiyan raged across Leyte and Samar, turning roads into rivers, and battered Cebu city, the country's second largest with a population of 2.5 million.
The eye of the storm - known locally as Yolanda - passed well to the south of the capital Manila, but the city still felt its force.
"The wind here is whistling. It's so strong and the heavy downpours are continuing," Mai Zamora, from the charity World Vision, in Cebu, told the BBC.
"We've been hearing from my colleagues in Tacloban that they've seen galvanised iron sheets flying just like kites."
Former BBC Manila correspondent Kate McGeown says that while reports are now coming in from some of the affected cities, there is still very little information from the countryside in large areas of the Visayas region such as Negros and Iloilo, and the island of Mindoro.
Typhoon Haiyan is now heading for Vietnam, as Darren Bett explains
There were reports of substantial damage even in areas that missed the worst of Haiyan, the 25th tropical storm to enter Philippine territory this year.
"The storm was very strong - although Surigao City was not directly hit we experienced its fury early this morning," said Protestant pastor Diosdado Casera in Surigao City in north-east Mindanao .
"The big buildings made of concrete were fine, but the houses made of wood and shingles and plywood have suffered a lot of damage, mainly to their roof."
Jeff Masters, meteorology director at the private firm Weather Underground, said in a blog post that the damage from Haiyan's winds must have been "perhaps the greatest wind damage any city on Earth has endured from a tropical cyclone in the past century".
In its path were areas already struggling to recover from a deadly 7.3-magnitude earthquake last month, including the worst-hit island of Bohol where about 5,000 people are still living in tents.
The UK's ambassador to the Philippines, Asif Ahmad, announced on Saturday that a team of humanitarian experts would be sent by the UK "to assess needs and then mobilise resources".
The head of the EU's delegation to the Philippines, Guy Ledoux, had earlier told local media that the EU was also sending a humanitarian aid team.http://www.bbc.co.uk/news/world-asia-24878801