The storm that made landfall in Quang Ninh Province on Tuesday has brought torrential rains to most of the country's north over the past few days, with rainfall exceeding 300 mm (11.8 inches) in several parts, according to the agency.
The deaths include seven in Son La Province, two in Dien Bien Province and one in the capital Hanoi, according to the agency.
Photos on state media showed flood waters had risen to the roofs of hundreds of houses in Dien Bien and washed away or buried roads in the area.
Floods and landslides have also inundated nearly 30,000 hectares of rice and cash crops and killed nearly 20,000 farmed cattle and poultry, the agency said.
Rains have subsided in northern Vietnam, according to the national weather agency, which forecasts a new heat wave in the area over the next days.