Although it has weakened to a tropical depression, authorities warned that more flooding and landslides could occur as the storm moves west.
In Yen Bai province, floods reached 1 metre (3 feet) high on Monday, forcing 2,400 families to evacuate to higher ground as water levels rose, AFP reported.
Yagi also sank and set adrift dozens of fishing boats. On Sunday, search and rescue workers found 27 people adrift at sea after 12 fishermen went missing.
About 50,000 people have been evacuated from coastal Vietnamese cities, and authorities have issued warnings to stay indoors.
Schools in 12 northern provinces, including Hanoi, have been temporarily closed.
Typhoon Yagi killed 24 people in southern China and the Philippines before hitting Vietnam.
Scientists say climate change is making typhoons and hurricanes stronger, more frequent, and staying over land longer. Warmer ocean waters mean storms absorb more energy, which leads to higher wind speeds.
Warmer air holds more moisture, which can lead to more rain.
