Hayden Panettiere’s cause of death remains a mystery after an autopsy was carried out on the Nashville and Heroes star following her sudden death aged 36.

The actress was found at her home in Greenville, South Carolina, on Sunday after police were called to the property.

Officers responded after an acquaintance reported that the star was “unresponsive” and in “cardiac arrest”.

Despite desperate efforts to revive her, her devastated family later confirmed her death.

Her father, Skip Panettiere, said in a statement: “It is with profound sadness that we share the tragic passing of our beloved Hayden.”

“She was an incredible light and a force of nature who brought immeasurable love and joy to all who knew her—and to the millions who watched her onscreen.”

He also asked that the family be given privacy as they “take time to process this unimaginable loss”.

Tributes have since poured in from heartbroken fans and Panettiere’s co-stars, including Oscar-winning actress Viola Davis, who described her as an "old, wise soul with such a deep heart".

A post-mortem examination has now been completed by the Greenville County coroner’s office, which said that “no signs of trauma were discovered that would have contributed to the death”.

However, her cause and manner of death have yet to be confirmed.

Officials are continuing to investigate the circumstances surrounding her death, with the coroner saying further tests must be completed before the cause can be determined.

Ms Panettiere leaves behind her 11-year-old daughter Kaya Klitschko.

The 36-year-old began acting as a child, appearing in soap operas before gaining wider recognition for her role in the 2000 sports drama Remember The Titans alongside Denzel Washington, and as the voice of Dot in Pixar’s 1998 film A Bug’s Life.

Panettiere later found fame playing cheerleader Claire Bennet in the superhero drama Heroes before going on to star as up-and-coming country singer Juliette Barnes for six seasons on the hit TV series Nashville.

Her performances in Nashville earned her two Golden Globe nominations for best supporting actress while her singing on the show produced 11 entries on the US Billboard Hot Country Songs charts.

Panettiere’s film credits include 2006’s Bring It On: All Or Nothing, comedy-drama film Raising Helen, and appearances in Scream 4 and Scream VI as Kirby Reed.

Paying tribute to Hayden, Viola Davis said: said: “What an amazing talent you were….so gifted. Julius and I loved working with you….an old, wise soul with such a deep heart.

“I wish the world had more time with you because I had a burning curiosity about who you were becoming. I saw this beautiful Phoenix rising from the ashes. Your tests became your testimony, and your testimony became your legacy.

“You will be remembered. Rest well. Sending healing prayers to your family, your daughter, and all who loved you. May they always speak your name…”

Bethany Joy Lenz – a long-time friend of Panettiere – said she was “crushed” by her death.

Sharing photos of the actress on set when she was young, as well as photos of them together over the years, the One Tree Hill star wrote: “There is nothing that posting pictures on the internet can do. I avoid it usually in moments like this. But I’m here with my head in my hands and I don’t know what else to do in aside from praying for her soul, which I have done and will continue.

“I’m crushed. I knew the wild little blonde. Was she nine? Ten? I was eighteen. She ran through the Screen Gem studio hallways at 222 E44th St. laughing and playing games in between blocking and camera rehearsals. Long, unruly curls trailing behind her. She knew her lines and everyone else’s. Her intelligence was astonishing. She understood scenes and nuance and human struggle like no child I’d ever seen on camera. And she’d sit with you for a great conversation, then giggle and go play.

“We’d connect on and off over the years, like the cousin in the family reunion who got famous and life moved her away – but I always felt such joy seeing her when we were lucky enough to cross paths. We’d make a pact to talk soon. Lunch. Dinner. Somewhere we could curl up into a corner – but we never quite made it happen. I mostly stayed up to date through mutual friends.”

Lenz went on to write that she “didn’t understand how this is real”.

“Everything seemed to be turning around. She was coming BACK to life, wasn’t she? It’s too young and there’s still so much more life. And her daughter…. Hayden, you are surround by love. I’m sorry for every moment I didn’t reach out or check in. This can’t be real.”

Concluding her tribute, she added: “These are moments of how I knew you, in glimpses over 27 years. I don’t know how to process this. I am praying for you to know the peace of God now and always.”