Oscar-winning actor and renowned comedian Robin Williams hanged himself in his California home and died by asphyxia, a coroner said on Tuesday based on preliminary findings.

Williams, 63, was found dead by his personal assistant at midday on Monday, suspended from a belt wedged between a door and a door frame in a seated position just of the ground, Marin County's assistant chief deputy coroner, Keith Boyd, told a news conference.

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

"His right shoulder area was touching the door with his body perpendicular to the door and slightly suspended. Mr. Williams at that time was cool to the touch with rigor mortis present in his body," Boyd added.

Officials also found a pocket knife near Williams and cuts with dried blood on his wrist that matched the knife blade.

Williams had been seeking treatment for depression, Boyd said. He would not discuss if had left a suicide note.

Funeral arrangements would be decided by the family, Boyd said. His body has been released by the coroner facility in neighboring Napa County.

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 collectively mourned on Tuesday the death of Robin Williams, the actor famous for his frenetic and freewheeling comedy whose apparent suicide prompted an outpouring of tributes.

Hollywood actors and Washington leaders alike declared themselves heartbroken by Williams' death on Monday at his home near Tiburon, north of San Francisco.

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.

Fellow comedic actor Steve Martin said in a tweet: "I could not be more stunned by the loss of Robin Williams, mensch, great talent, acting partner, genuine soul."

Late-night talk show host Conan O'Brien found out about Williams' death during the taping of his show Monday and broke the news to the audience.

"This is absolutely shocking and horrifying and so upsetting on every level," said a visibly shaken O'Brien, adding "we're thinking about everybody who he touched around the world throughout his life and we're thinking about Robin tonight."

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

But many questions remained over his final months and what could have led to his apparent suicide.

U.S. President Barack Obama paid tribute to Williams on Monday, saying "he arrived in our lives as an alien - but he ended up touching every element of the human spirit."

On Tuesday, his secretary of state, John Kerry, remembered that his impact went far beyond his profession.

"He loved people and he committed himself to any issue that concerned him. Robin wasn't just a huge creative genius but a caring, involved citizen," Kerry said in a statement.

On the Hollywood Walk of Fame, dozens of fans congregated around Williams' star early Tuesday, leaving flowers and candles to remember the versatile actor.

'DOCTOR OF THE SOUL'

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. Their show was canceled in May after one season.

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

Williams, who was born in Chicago in 1951 and grew up in suburban Detroit earned four Academy Award nominations, the first for his portrayal of U.S. Army radio announcer Adrian Cronauer during the Vietnam War in "Good Morning, Vietnam."

He also was nominated for the 1990 coming-of-age prep school drama "Dead Poets Society" and 1991's "The Fisher King." His other notable films included "Mrs. Doubtfire," "Patch Adams," "The Birdcage," "Awakenings" and "The World According to Garp."

Williams will appear in the upcoming film "Night at the Museum: Secret of the Tomb," playing the statue of Teddy Roosevelt who comes to life at night, and the holiday comedy "Merry Friggin' Christmas." He also was attached to a sequel to his 1993 hit "Mrs. Doubtfire."

Williams married three times, most recently in 2011 to Susan Schneider. He had three children.

Williams had lived many years far from the hype of Hollywood and was known to his neighbors as a kind man who would ride his bike and wave to everyone.

"Everyone loved him, but nobody bothered him. He would live unrecognized and just keep to himself," said Johanna Denning, a neighbor who often saw Williams riding his bike amid low-slung houses with views of the San Francisco Bay.

Sonja Conti said the actor would often ask about her dog, which he nicknamed "Dude." Having Williams around "wasn't like having a celebrity. He was just a normal, nice guy," she said. "People left him alone."

He was fond of dropping in on a local venue to try out his latest material and "embodied what it meant to be humble," said Lucy Mercer, executive artistic director at Throckmorton Theatre.

But back on Hollywood's comedy circuit, those who worked with him and were inspired by him struggled to process his loss.

Jamie Masada, founder and owner of The Laugh Factory who knew Williams for 35 years, called him a "doctor of the soul."

"Even if you just saw him a few times on TV, you still cared for him like you knew him, like he was your family," Masada said. "Not too many people have that presence or life." 

Reuters, Los Angeles Times