US officials say 40,000 people may have been infected with HIV and hepatitis in a major health scare, after a Las Vegas clinic was found to have reused syringes and medicine vials.

Authorities in southern Nevada said they were notifying some 40,000 patients who received anaesthesia injections at the clinic's endoscopy centre between March 2004 and January 11, 2008 about potential exposure to hepatitis and HIV.

They recommended in a statement that the patients "contact their primary care physicians or health care providers to get tested for hepatitis C as well as hepatitis B and HIV".

The move comes after several acute cases of hepatitis C showed up in the area.

Six people have been diagnosed with the disease since January, which is three times higher than the yearly average for the Las Vegas region.

The three first cases came to light in January, and three other patients were subsequently found to have been infected with hepatitis C.