Television footage today showed inundated houses and streets in the town of Hoi An and the former imperial City of Hue, both classed as UNESCO World Heritage Sites, where hundreds of tourists have been evacuated over recent days.
At least 34 people have been killed over several days of flooding which were the most destructive since 1999, a regional official said.
"Eleven other people are missing. More than 100,000 houses have been flooded and transport by road, air and rail has been severely affected across the region," said Nguyen Quang Trung, an official in the coastal city of Danang, adding several central provinces had been hit.
Local authorities yesterday said around 20,000 people were evacuated after at least six deaths during the floods, caused by heavy rain from a new tropical depression in the South China Sea.
Hundreds of thousands of people were evacuated last weekend before the arrival of Typhoon Haiyan which wreaked devastation on the Philippines, before tearing across the South China Sea.
But the communist nation was spared the worst of the typhoon's power as it weakened before striking Vietnam's coast.