The incident happened at Hoa Binh Province General Hospital, 80km west of Hanoi.
Eighteen people were being treated when some felt sick and breathless. The victims were suspected to have suffered anaphylactic shock, the state-controlled media reported.
A criminal investigation has been opened.
All medical equipment and drugs in the kidney care department had been sealed off at the state-run hospital.
“The remaining patients were really lucky … all of them were in shock,” said Quang, whose cousin had come for dialysis before treatment was cancelled.
“I would like to apologise to families and the whole community; we are very surprised at this rare incident,” said hospital director Truong Quy Duong, according to the state-run media.
The 18 patients were receiving routine dialysis, a process that cleans the blood and removes waste, which often involves passing blood through a machine, if people’s kidneys have stopped working sufficiently well.
A doctor spoke of the “nightmare” as he struggled to keep the patients alive. “It’s a huge loss. I feel pain as if I had lost members of my own family,” said Dr Hoang Cong Tinh.
Le Tien Dung, whose 47-year-old wife is in intensive care, told AFP that she had fallen ill during the procedure.
“She became itchy all over her body, she had a stomach ache,” he said. “My biggest hope is that my wife will overcome this.”
The remaining 10 patients are being tested in Hanoi and are reportedly stable.
In December, a seven-year-old girl died in southern Ca Mau province after being injected with antibiotics to treat a respiratory ailment. During the same month two people died at a Hanoi hospital when being put under anaesthesia before surgery. In 2013, three children died in Quang Tri after being injected with the wrong vaccinations.
Relatives of the seven victims had been paid US$660, the authorities announced.
Government hospitals tend to have lower quality of care than private clinics, especially in rural areas.
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