US actor Robin Williams was in the early stages of Parkinson's Disease before his death, according to a statement released by his widow.

Susan Schneider said the actor "was not yet ready to share publicly" his struggles with the degenerative disease.

In a statement, Ms Schneider said "Robin's sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson's Disease, which he was not yet ready to share publicly."

She added that Williams' family hoped others would to use his tragic death to seek any help they needed "to treat whatever battles they are facing so they may feel less afraid".

The Oscar-winning Hollywood star took his own life earlier this week. The cause of death was suicide due to asphyxia, according to a preliminary investigation.

The actor and comedian (63) was discovered in a bedroom by his personal assistant who had become concerned and entered the room before midday on Monday.

The celebrity was last seen alive by his wife at about 10:30pm Sunday evening before she went to bed.

She then retired to another bedroom and when she left the property in the morning, she thought he was asleep, before his PA found him and raised the alarm.

Marin County Sheriff's Lieutenant Keith Boyd said toxicology tests will be performed and the investigation was ongoing.

The US star of hit movies including Good Will Hunting, Mrs Doubtfire and Good Morning, Vietnam had recently grappled with severe depression.

He battled addiction for decades and checked himself back into rehab last month.

Anyone feeling emotionally distressed or suicidal can call Samaritans for help on 116-123, or email jo@samaritans.org