Police in downtown Hoan Kiem District said Monday that around midnight on Sunday, the woman, who was riding her motorbike, had stopped at a red light at the intersection of Tran Hung Dao and Ba Trieu streets.
At that moment, a group of 20-30 motorbikes, traveling at high speeds and against the flow of traffic, approached the intersection.
One motorbike in the group struck the woman, throwing her onto the road, where she died instantly. The group then fled the scene.
Police identified one of the riders as 19-year-old Nhung, who was riding a motorbike carrying her friend Phuong Anh, also 19. According to police reports, Nhung's bike collided with the woman, and a second motorbike carrying two more individuals also hit the victim.
Nhung told police on Tuesday that she and her friends had been riding through Hanoi's streets on Saturday night to take photos. Near the Hanoi Opera House, they joined the larger group of motorbike racers out of curiosity, hoping to spot acquaintances among them.
As they approached the Tran Hung Dao intersection, Nhung's motorbike collided with the victim, causing both her and Phuong Anh to fall to the ground.
Nhung said she woke up in the hospital the next morning and learning that the crash had resulted in the woman's death.