Six people are dead and 12 others have been sent for treatment after undergoing kidney dialysis at a hospital in Vietnam on Monday, health officials said.
The victims were suspected to have suffered anaphylactic shock, state media reported, as officials launched an investigation into the incident.
All 18 patients were being treated for kidney failure at the state-run Hoa Binh Province General Hospital, when after 45 minutes on dialysis some reported nausea, abdominal pain and shortness of breath.
"The hospital and police have sealed off all the machines, equipment and medicine in the nephrology department," a statement from the health ministry said.
The department has also stopped receiving new patients, and the families of the deceased will be given $660 as compensation.
The ministry has sent a team to the area, 80 kilometres (50 miles) southwest of Hanoi, to investigate the incident.
"Individuals or groups who violated (regulations) will be strictly handled," the statement said.
Most hospitals in Vietnam are state-run, though private facilities are increasingly common in the communist country.
Standards of care at private hospitals tend to be better than at their government-run counterparts, but they are generally seen as safe and medical malpractice deaths are relatively rare in Vietnam.