Law enforcement officials say Oscar winner Philip Seymour Hoffman was found with a syringe in his arm and a drug overdose is suspected as his cause of death.
The two officials spoke to The Associated Press on condition of anonymity because they are not authorised to speak about evidence found at the scene.
The officials say glassine envelopes they suspect contained heroin were also found in Hoffman's New York City apartment. Those items are being tested.
They say Hoffman's body was discovered by two people: a friend who made the 911 call and his assistant.
Philip Seymour Hoffman, who won a best actor Oscar in 2006 for his portrayal of writer Truman Capote in Capote and created a gallery of other vivid characters, many of them slovenly and slightly dissipated comic figures, has died. He was 46.
Hoffman spoke candidly over the years about past struggles with drug addiction. After 23 years sober, he admitted in interviews last year to falling off the wagon and developing a heroin problem that led to a stint in rehab.
The law enforcement officials said Hoffman's body was discovered in a bathroom at his Greenwich Village apartment by a friend who made the 911 call and his assistant.
Late Sunday (Monday morning, NZ time), a police crime-scene van was parked out front, and technicians carrying brown paper bags went in and out. Police kept a growing crowd of onlookers back. A single red daisy had been placed in front of the lobby door.
Hoffman's family called the news "tragic and sudden."
"We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone," the family said in a statement.
Hoffman - no matinee idol, with his lumpy build and limp blond hair - made his career mostly as a character actor, and was one of the most prolific in the business, plying his craft with a rumpled naturalism that also made him one of the most admired performers of his generation. He was nominated for Oscars four times in all.
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 that he would eventually appear in.
He often played comic, slightly off-kilter roles in movies like 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. And 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.
Born in 1967 in Fairport, NY, Hoffman was interested in acting from an early age, mesmerized 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.
"Hoffman is only 44, but he nevertheless sags in his brokenness like a man closer to retirement age, lugging about his sample cases filled with his self-denial and disillusionment," Kennedy wrote. "His fraying connection to reality is pronounced in this production, with Hoffman quick to anger and a hard edge emerging from his babbling."
Two films starring Hoffman premiered last month at the Sundance Film Festival: the espionage thriller A Most Wanted Man, directed by Anton Corbijn, and God's Pocket, the directorial debut of John Slattery.
Hoffman is survived by his partner of 15 years, Mimi O'Donnell, and their three children.