Five people died in Son La and two others were killed in Dien Bien following the downpours.
Rescue workers are also searching for 10 others reported missing in the mountainous provinces, officials added.
According to Tuoi Tre newspaper, flash floods early Thursday swept away 10 houses and damaged eight homes in Muong Pon commune of Dien Bien province.
It has rained heavily in northern Vietnam since Tuesday, and many areas including the outskirts of the capital Hanoi are filled with muddy floodwater.
Between June and November, Vietnam is often struck by downpours, triggering flooding and landslides.
But scientists have warned that extreme weather events globally are becoming more intense and frequent due to climate change.
In mid-July, a landslide triggered by heavy rains killed 11 people travelling in a van in northern Ha Giang province.
Last year, natural disasters left 169 people dead or missing in the Southeast Asian country.
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