Tributes have been paid to Oscar-winning actor Philip Seymour Hoffman, who was found dead in his Manhattan apartment yesterday.

Hoffman was one of the leading actors of his generation and won an Academy Award for his title role in the film 'Capote'.

A New York police source has described his death as an apparent drug overdose.

Hoffman, 46, was discovered unresponsive on the bathroom floor of his Greenwich Village apartment by police responding to a 911 call.

Emergency Medical Service workers declared him dead at the scene, New York City police said in a statement.

An investigation is under way.

A police spokesman said investigators found Hoffman with a syringe in his arm and recovered two small plastic bags in the apartment containing a substance suspected of being heroin.

Hoffman, who is survived by three children with his partner Mimi O'Donnell, had detailed his struggles with substance abuse in the past.

"We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone," Hoffman's family said in a statement issued through his publicist.

"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," it added.

CNN, citing a law enforcement official, reported that Hoffman was last seen alive at 8pm Saturday.

He had been expected to pick up his children yesterday but failed to show up, prompting playwright David Katz and another person to go to his apartment, where they found him dead, CNN said.

Hoffman spoke in the past of struggling with drugs, including a 2006 interview in which he told CBS he had at times abused "anything I could get my hands on. I liked it all".

Workmanlike intensity

Born in upstate New York near Rochester, Hoffman won the Best Actor Oscar for the 2005 biographical film 'Capote', in which he played writer Truman Capote.

He also received three Academy Award nominations as best supporting actor, for 'The Master' in 2013, 'Doubt' in 2009 and 'Charlie Wilson's War' in 2008.

After more than a dozen earlier roles, Hoffman burst onto the film scene in 1997's 'Boogie Nights', in which he played a lovelorn gay man in a movie about the porn industry.

Hoffman, who brought a workmanlike intensity to his roles, often played characters with innate intelligence and logical minds riven by underlying passion.

The actor's on-screen persona could range from professorial to unkempt, from the aloof intellectual to the everyman.

Hoffman appeared in blockbusters such as 'Twister' and 'The Hunger Games' series.

But he was more often associated with the independent film world for his portrayals of often disturbing and complex characters in such films as 'Happiness', in which he played an obscene phone caller, and 'Before the Devil Knows You're Dead'.

In the latter, he played a son who schemes to rob his parents' jewellery store, resulting in their deaths. Hoffman could also play nice, as in his portrayal of an angelic nurse in 'Magnolia'.

Other noteworthy films included 'Moneyball', 'The Savages', 'Cold Mountain' and 'Scent of a Woman', one of his earliest films.

Lionsgate, the studio behind 'The Hunger Games', called Hoffman "one of the most gifted actors of our generation".

"We're very fortunate that he graced our 'Hunger Games' family. Losing him in his prime is a tragedy, and we send our deepest condolences to Philip's family," the studio said in a statement.

Hoffman also frequently appeared on Broadway, earning Tony award nominations for his role as the main character Willy Loman in 'Death of a Salesman', and for his parts in 'Long Day's Journey Into Night' and 'True West'.

"If you missed him as Willy Loman, you missed a Willy Loman for all time," actor Steve Martin said on Twitter yesterday.

"This is a horrible day for those who worked ‎with Philip," Tom Hanks, who co-starred with him in 'Charlie Wilson's War', said in a statement.

He added: "He was a giant talent. Our hearts are open for his family."

British comedian Russell Brand, who has discussed his own struggles with drug abuse, offered his sympathies to Hoffman's family on Twitter.

"Addiction kills, I hope all who need it have access to abstinence based recovery," he wrote.

Showtime, the cable television network that had just ordered a ten-episode comedy, 'Happyish', starring Hoffman and produced by his company, Cooper's Town Productions, mourned the loss of the talented actor.

"Philip Seymour Hoffman was one of our generation's finest and most brilliant actors. He was also a gifted comedic talent. It was a great privilege and pleasure to work with him and we are all absolutely devastated by this sudden loss," it said.

Hoffman appeared last month at the Sundance Film Festival in Utah for the premiere of 'A Most Wanted Man', an espionage thriller based on the John le Carre novel in which he played German spy Gunther Bachmann.

At the premiere, Hoffman told Reuters that he connected to Gunther's personality, a man driven by the shame of previous failure into an obsessive pursuit of capturing terrorists by any means necessary.

"I think it'd be hard for anyone not to connect with the loneliness. He's pretty lonely, driven, obsessive guy, unforgiving of himself in a lot of ways. A lot of traits that a lot of people carry in one grade or another," Hoffman said.

New York Mayor Bill de Blasio said via Twitter: "Saddened by Philip Seymour Hoffman's tragic and untimely passing. Today New York mourns the loss of one of stage and screen's greats."