Heavy rains have been pounding central Vietnam for days. Local media say at least 17 people have died and 13 others remain missing.
The downpours brought by a low pressure system have inundated Hoi An Ancient Town, which is recognized as a UNESCO World Heritage site for its historic streetscapes.
About 33,000 buildings, including homes, reportedly have been submerged, and more than 30,000 people displaced.
Footage on Sunday from a central town shows a person being rescued by helicopter from a ship surrounded by a torrent of muddy water. People are also seen evacuating on foot or by boat through waist-high water.
As a storm made landfall in Vietnam, it released more heavy downpours. Authorities are calling on people to evacuate.
Natural disasters, mostly floods and landslides triggered by storms, killed 132 people and injured 207 others in Vietnam last year, according to the VNExpress.