More than 200,000 people have crammed into storm shelters and soldiers are helping reinforce vulnerable homes as a super typhoon bears down on Vietnam after leaving a deadly trail of devastation in the Philippines.
Haiyan, one of the most intense typhoons on record, slammed into the Philippines on Friday with sustained winds of about 315km/h.
It is expected to make landfall in central Vietnam early on Sunday, with millions of people thought to be in its path.
Authorities have begun mass evacuations in at least four central coastal provinces, Vietnam's state-run VNExpress news site said on Saturday, as the country was put on high alert.
"More than 200,000 people have evacuated to shelters - some shelters are overloaded," VNExpress said.
The army has been mobilised to provide emergency relief with some 170,000 soldiers assisting people after the typhoon hits.
Many schools in the affected area - normally open at the weekends - have closed, as people from vulnerable low-lying coastal villages move to higher ground.
Images in state media showed women, children and the elderly crowded into typhoon shelters.
The Red Cross has said Haiyan is likely to be a category two or three typhoon and warned that some 6.5 million people in Vietnam could be affected.
Central Vietnam has recently been hit by two other typhoons - Wutip and Nari, both weaker category one storms - which flooded roads, damaged sea dykes and tore the roofs off hundreds of thousands of houses.
"Typhoon Haiyan is two or three times more powerful than either typhoon Wutip or Nari and it is expected to do more damage," Michael Annear, Red Cross country representative, told AFP.
"We're expecting a lot of wind damage ... especially for those who repaired their houses themselves after Wutip and Nari."
Annear added that heavy rain could put hydro-electric reservoirs or dams at risk and warned of potential flash flooding.
"Hundreds of people have flocked to hardware stores ... Customers are snapping up plastic sheeting, wire and nails," the official Thanh Nien newspaper said.
Although Haiyan is expected to weaken slightly, it is still considered a super typhoon with the potential for "complicated developments", said Prime Minister Nguyen Tan Dung at an urgent meeting on Friday.
Dung, who is personally overseeing preparations, has called all Vietnamese vessels back to shore and ordered hydropower reservoirs to step up safety measures "to limit the consequences in terms of human and materials", a notice on the government's official website said.
National flag carrier Vietnam Airlines has advised passengers to be prepared for flights to be interrupted or cancelled on Sunday.
The scale of the damage wrought by Haiyan in the Philippines was still emerging Saturday, with many of the worst-hit towns cut off from communications, but early reports raised fears of mass casualties.
Energy Secretary Jericho Petilla said he thought "hundreds" of people had been killed in the coastal town of Palo and surrounding villages after visiting the eastern island of Leyte on Saturday.
