Their names and nationalities have not been revealed but preliminary information from the local police was that they were from Western Europe.
At around 5 p.m. they were riding on National Highway 1A in Tam Diep Town, two hours south of Hanoi, when a truck carrying construction materials hit them from behind.
The woman died on the spot after being dragged under the truck while the man fell and was hospitalized with serious injuries.
Local authorities said the gloomy weather and heavy rains had caused poor visibility at the time of the accident.
Road crashes are a leading cause of death in Vietnam, killing almost one person every hour. More than 18,720 accidents occurred last year, killing 8,244 people and injuring nearly 14,800, according to the National Traffic Safety Committee.