prince dead
Prince at the French  Open in Paris on June 2, 2014. Getty

Prince may have overdosed on what was likely heroin or narcotic painkillers and was then given a so-called "save shot" six days before his death, TMZ is reporting, citing several unnamed sources.

"Save shots" usually help combat opiates such as heroin and narcotic painkillers in the bloodstream. Doctors and paramedics have used the injectable medication, called naloxone, for years.

Authorities have yet to determine the cause of death of the 57-year-old music legend who was found unresponsive in his Paisley Park recording studio in suburban Minneapolis, Minnesota. Post-mortem results are pending.

A medical emergency forced Prince's jet to land in Illinois on Friday (15 April) as he was heading home to Minneapolis from a concert in Atlanta, Georgia. Representatives told TMZ at the time he was suffering from the flu.

But that's when he was given the "save shot" and doctors recommended he stay in hospital for 24 hours, TMZ reports. However, Prince checked himself out in just three hours, apparently because the hospital couldn't meet his demand for a private room. When he left he "was not doing well", a source told TMZ.

Prince had cancelled two performances earlier in the month, and his representatives cited health issues without offering any details.

Minnesota authorities are reportedly attempting to obtain Prince's health records from Moline, Illinois, where the hospital is located.

A 911 call unearthed by TMZ revealed that a witness, who may have been one of the first to find Prince unresponsive, believed him dead even before the first responders arrived.

"Um, we're at Prince's house," the man said on the call. "So, yeah, um, the person is dead here."

As tributes to the creative icon poured in from around the world, Prince's sister Tyka Nelson spoke briefly to a crowd of mourners who amassed outside his recording studio. "Thank you for loving him," she said. "He loved you all."