Kyle Busch Was Coughing Up Blood Day Before Death, According to 911 Call

Kyle Busch's medical emergency has been partially revealed by 911 audio obtained by TMZ Sports ... with a caller saying the NASCAR superstar was struggling to breathe, overheating and coughing up blood before medics rushed to help.

During the emergency call placed around 5:30 PM Wednesday, the caller urgently requests an ambulance to a training facility in Concord, North Carolina ... telling dispatch, "I've got an individual that's shortness of breath, very hot, thinks he's going to pass out, and he's producing a little bit of blood, coughing up some blood."

The caller also confirmed the patient was still conscious at the time ... repeatedly telling dispatch, “He is awake. He's awake. He's awake.”

Kyle was known to use this testing facility extensively since joining Richard Childress Racing -- and according to the audio, he was lying on a bathroom floor inside the complex while employees prepared for paramedics to arrive.

The caller even asked responding crews to shut off their sirens when approaching the building ... while explaining he would wait outside and flag them down at a side entrance.

TMZ also obtained dispatch audio from the incident ... listen to it above.

As we reported ... Busch reportedly became unresponsive Wednesday while testing in a Chevrolet racing simulator ... just one day before his death at 41.

He was transported to a Charlotte-area hospital after collapsing during the simulator session ... though officials have not yet confirmed his exact cause of death.

The shocking collapse came less than two weeks after Busch reportedly requested medical assistance during a race weekend at Watkins Glen, where he had been dealing with what was described as a severe sinus-related illness.

Busch's death sent shockwaves through the racing world Thursday ... with tributes pouring in from NASCAR drivers, teams and fans mourning one of the sport’s most dominant modern stars.