The rain at 2 p.m. lasted for about an hour, causing water levels to rise up and rush towards downtown areas.
Several homes were flooded, and some streets were 30-50 cm deep underwater, causing vehicles to fail.
Sa Pa has emerged in recent years as a popular tourist town, one hour from Indochina's highest peak Fansipan. However many travel lovers have mourned the loss of nature to rapid construction in town.
In Hanoi, an afternoon rain also uprooted trees, causing them to fall onto cars being parked on Hoang Ngan and Le Van Luong streets. Congestion ensued, though there were no casualties.