LOS ANGELES  —  The city of Las Vegas has shut down a clinic where up to 40,000 people may have been exposed to hepatitis C and the HIV virus through the reuse of syringes and vials, officials said on Sunday.

The clinic at the heart of the scandal, the Endoscopy Center of Southern Nevada, "was served with an emergency suspension of its business license," city authorities said in a statement.

Officials are asking about 40,000 people to be tested for hepatitis B and C and HIV because of unsafe medical practices at the clinic.

Health authorities launched an investigation into the clinic after six former patients were diagnosed with hepatitis. Nurses at the clinic were told "to reuse syringes when administering anesthesia" and "to reuse vials of medication," the city said, citing a probe by public health agencies.

The local prosecutors' office said it was closely examining the case and raised the possibility of filing charges against the center.

"It won't happen tomorrow or the next day, but we are taking a hard, fast look at all the facts in the case," District Attorney David Roger told KLAS-TV.

Some former patients had contacted lawyers for a possible class action suit against the clinic, local media reported.

The clinic did not comment directly on the allegations but expressed concern for patients infected and said it had undertaken new precautions.