A doctor and three nurses were attacked with tear gas at a hospital in the central province of Nghe An on Friday morning, local news website Vietnamnet reported.
Nguyen Thi My Hoa, one of the victims, said the four were working in the Vinh Hospital of Transport's blood dialysis room when two men in black came, asking to meet Dr. Nguyen Thi Thu Lan.
When Lan asked them to enter the room, the strange men sprayed them with tear gas, affecting ten patients as well, the nurse told Vietnamnet.
Local newspaper Tuoi Tre quoted an unnamed source as saying that Lan had received threatening text messages last week. The doctor then reported the threats to local police and took a leave until Friday.
Police have launched an investigation into the case.