Police have also stepped up surveillance and patrols along the cars-only Ho Chi Minh City-Long Thanh-Dau Giay Expressway to detect similar cases.
Late last month, a driver said someone hurled stones at his car and broke the windshield after he passed the Long Thanh Bridge, near the Long Phuoc toll station.
Earlier on September 11, 2015, Tran Bao Long said he was driving a bus on the highway when he was similarly attacked. A window was broken but luckily no one was hurt, he said.
Several other drivers have also reported stone attacks on the highway.
Nguyen Thi Hoai Phuong, deputy director of Vietnam Expressway Services Engineering JSC, which manages the highway, confirmed that many vehicles have been damaged after stones were thrown at them.
Phuong said such attacks are extremely dangerous on highways because cars are driving at high speed. The speed limit on HCMC-Long Thanh-Dau Giay Expressway, for instance, is 125 kilometers per hour.