Award-winning actor Philip Seymour Hoffman had a syringe in his arm when his body was found in his apartment in New York City.

The 46-year-old was found in his bathroom in the city's Greenwich Village area at 11.30am local time on Sunday (3.30am AEDT on Monday).

The New York Police Department is investigating, and the Office of the Chief Medical Examiner is to determine the exact cause of death.

"It appears to be an alleged overdose," a police official said.

The actor was found on the bathroom floor, wearing shorts and a T-shirt, the officer added.

Investigators found a syringe in his left forearm, at least two plastic envelopes with what appeared to be heroin nearby, and five empty plastic envelopes in a rubbish bin, the official said.

"It’s pretty apparent that it was an overdose," the official said. "The syringe was in his arm."

He said the actor had been alone. There were no pills and no sign that the actor had been drinking, he added.

Hoffman, 46, won the Academy Award for best actor for the 2005 biographical film Capote, and received three Academy Award nominations as best supporting actor.

Hoffman is survived by partner Mimi O'Donnell, a costume designer, and their three children, son Cooper Alexander, 10, and daughters Tallulah, 7, and Willa, 5.

His family released a statement, saying: "We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone.

"This is a tragic and sudden loss and we ask that you respect our privacy during this time of grieving. Please keep Phil in your thoughts and prayers."

An unnamed police official said Hoffman had been found by a friend who had become concerned about not being able to reach him.

Hoffman checked into rehab in May for heroin use.

A woman answering the phone at Hoffman's New York production company declined to comment.

"I don't have a comment at this time on that, thank you,'' she said.

Speaking at the London Critics' Circle Film Awards in central London, John Hurt - who starred with Hoffman in the 2003 film Owning Mahowny - said: "It's a devastating loss. His contribution was massive.''

A crowd of journalists and neighbours gathered, and a red rose and a bouquet of white roses were laid at the entrance.

One neighbour who gave her name as Janine, said she was accustomed to seeing the actor and his family out and about.

"They were always in the 'hood," she told AFP. "My husband saw him last week ... They were a part of the community here."

Hoffman made his career mostly as a character actor.

In one of his earliest films, he played a spoiled prep school student in Scent of a Woman in 1992. One of his breakthrough roles came as a gay member of a porno film crew in Boogie Nights, one of several movies directed by Paul Thomas Anderson in which he would eventually appear.

He often played comic, slightly off-kilter roles in movies such as Along Came Polly, The Big Lebowski and Almost Famous. More recently, he was Plutarch Heavensbee in The Hunger Games: Catching Fire and was reprising that role in the two-part sequel, The Hunger Games: Mockingjay, which is in the works. In Moneyball, he played Art Howe, the grumpy manager of the Oakland Athletics who resisted new thinking about baseball talent.

Just weeks ago, Showtime announced Hoffman would star in Happyish, a new comedy series about a middle-aged man's pursuit of happiness.

In The Master, he was nominated for the 2013 Academy Award for best supporting actor for his role as the charismatic leader of a religious movement. The film, partly inspired by the life of Scientology founder L. Ron Hubbard, reunited the actor with Anderson.

He also received a 2009 supporting nomination for Doubt, as a priest who comes under suspicion because of his relationship with a boy, and a best supporting actor nomination for Charlie Wilson's War, as a CIA officer.

In 2010, he directed a Sydney Theatre Company production of True West, starring Brendan Cowell.

Born in 1967 in Fairport, New York, Hoffman was interested in acting from an early age, mesmerised at 12 by a local production of Arthur Miller's All My Sons. He studied theatre as a teenager with the New York State Summer School of the Arts and the Circle in the Square Theatre. He then majored in drama at New York University's Tisch School of the Arts.

Trained in the theatre, with a versatility and discipline more common among British performers than Americans, he was a character actor who could take on any role, large or small, loathsome or sympathetic.

On the stage, he performed in revivals of True West, Long Day's Journey Into Night and The Seagull, a summer production that also featured Meryl Streep and Kevin Kline.

In 2012, he was more than equal to one of the great roles in American theatre - Willy Loman in Death of a Salesman, a performance praised as "heartbreaking" by Associated Press theatre critic Mark Kennedy.

"I try to live my life in such a way that I don’t have profound regrets,’’ Hoffman told The New York Times in 2008. "That's probably why I work so much. I don't want to feel I missed something important."

Agencies, smh.com.au