Oscar-winning actor and renowned comedian Robin Williams took his own life in his California home, a coroner said, based on preliminary findings.

Williams, 63, was found dead by his personal assistant just before midday on Monday (local time), Marin County’s assistant chief deputy coroner, Keith Boyd, told a news conference.

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“Mr Williams’ personal assistant became concerned at approximately 11:45 am when he failed to respond to knocks on his bedroom door,” Mr Boyd said.

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Mr Boyd said Williams had been seeking treatment for depression.

Williams made two attempts on his life in his final hours, according to details released by the Marin County Sheriff’s Department.

It has also been confirmed that the comedian did not leave a suicide note.

He said funeral arrangements would be decided by the family and that his body had been released by the coroner facility in neighbouring Napa County.

Mr Boyd would not say if any drugs or alcohol were involved and that the full toxicology report would take several more weeks, stressing that the investigation was continuing.

Comedians, politicians and several generations of fans are collectively mourning the death of Williams, famous for his frenetic and freewheeling comedy.

The news of Williams’ death rippled across social media, stunning fans young and old and comedians who had been influenced by Williams since he broke out in the 1970s TV comedy Mork & Mindy as a strange and lovable creature from outer space.

Williams had been open about his struggles with alcohol and cocaine and in the past months had entered a rehabilitation centre to help him maintain sobriety.

But many questions remain over his final months and what could have led to his death.

On the Hollywood Walk of Fame, dozens of fans congregated around Williams’ star early on Tuesday (local time), leaving flowers and candles to honour the versatile actor.

Williams’ appeal stretched across generations and genres, from family fare as the voice of Disney’s blue Genie in Aladdin to his portrayal of a fatherly therapist in the 1997 drama Good Will Hunting, for which he earned his sole Oscar.

The death of Williams shook Hollywood, and colleagues mourned the loss of what many called a big-hearted man and one of the most inventive comedians of his time.

Sarah Michelle Gellar, who played his daughter in the recent CBS television comedy, The Crazy Ones, said her life was better for knowing Williams.

“To my children he was Uncle Robin,” Gellar said in a statement.

“To everyone he worked with, he was the best boss anyone had ever known, and to me he was not just an inspiration but he was the father I had always dreamed of having.”

– with ABC