A technician at the Zhejiang Provincial Hospital of Traditional Chinese Medicine re-used a tube employed in an earlier medical exam for an HIV-positive patient, the province's health and family planning commission said in a statement on its official website, calling it a "severe violation of procedure".
The local centre for disease control confirmed that five patients were infected, it added, without offering further information about the total number of patients the technician may have exposed to the virus.
It was not clear what those who were accidentally infected were originally being treated for.
As of this afternoon, the hospital's website had been taken offline. No hospital representatives could be reached for comment.
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Most Chinese-language media reports about the accidental HIV infections had been deleted by Thursday afternoon, leaving only the short government statement in online circulation.
Many critical comments on social media had been removed.
One user "shocked" by the incident noted that posts about it were rapidly being deleted and that major Chinese news outlets had disabled comment and forwarding functions on their online reports.
Calling the censorship disgusting, the user added: "I think people have the right to know the truth."
In a 2015 report China told the UN that it had 501,000 cases of HIV/AIDS as of the end of 2014.
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