The storm struck northeastern Vietnam's Quang Ninh province, about 75 miles from Hanoi about 5 a.m. Beijing time, China's meteorological administration said.
Vietnamese forecasters issued a severe tropical storm warning, predicting about 4 inches of rain accompanied by gale-force winds in parts of Quang Ninh and Lang Son province.
Vietnamese officials said at least five people died while preparing to escape the storm, the Vietnam News reported.
Government officials toured several Vietnamese provinces to inspect preparations for Haiyan, forecast to make landfall Sunday or Monday.
Deputy Prime Minister Hoang Hai urged provincial authorities to call all fishermen to shore and evacuate residents living in coastal areas to safer places.
In the Philippines, where officials fear thousands of people may have died, devastation and corpses strewn about Tacloban after Typhoon Haiyan blew through Friday prompted one person to compare the Philippine city to a apocalyptic movie.
The man, who declined to be identified, told PhilippineInquirer.net the aftermath of Haiyan, known in the Philippines as Yolanda, reminded him of the movie "World War Z," film depicting the world as it was being taken over by animated corpses or zombies.
"Everywhere we look, we see dead bodies on the streets," said the witness, who was in the city for a seminar.
An official death toll was not available, but the Red Cross put the toll around 1,200, while a local mayor said as many as 10,000 people may have died in his area alone, CNN reported.
Officials had not been able to get to remote areas made even more inaccessible by the storm, so the death toll could be significantly higher, CNN said.
Tacloban Mayor Alfred Romualdez told CNN it is "entirely possible" as many as 10,000 people died during the storm in just Leyte province.
Tacloban City Administrator Tecson Lim said most of the city's houses were damaged or destroyed and more than 300 bodies had been recovered so far, The New York Times reported.
Haiyan inundated many areas in Leyte, Eastern Samar, Western and Central Visayas, Bicol and Northern Mindanao regions.
"The devastation here is absolute," Interior Secretary Manuel Roxas II told the reporters upon landing at Tacloban airport Saturday.
The C-130 military plane that bought Roxas also carried relief supplies and equipment.
Besides buffeted by strong winds, Tacloban also experienced storm surges that swamped the airport near the coastlines. PhilippineInquirer.net said the flood reached the ceiling of airport offices, drowning people inside.
Roxas said Saturday restoring power and communications would take time because engineers were having difficulty tracing the ends of cable wires providing electricity and cell signals.
The Philippine disaster relief agency said Sunday about 4.4 million people were homeless in areas hit by the superstorm, China's state-run news agency Xinhua reported.
Philippine President Benigno Aquino III flew to Tacloban Sunday to join Roxas to inspect the area and distribute humanitarian aid.
Xinhua said Britain would provide about $9.58 million to aid in the relief effort.