Philip Seymour Hoffman was found dead in his New York apartment (Victoria Will/Invision/AP)

Actor Philip Seymour Hoffman died from a toxic mix of heroin and other drugs, US officials said.

A spokeswoman for the New York City medical examiner said that Hoffman died from a mix of heroin, cocaine, amphetamines and benzodiazepines, which are psychoactive drugs such as Librium.

The death was ruled an accident. Police had been investigating his death as a suspected drug overdose.

Law enforcement officials have said Hoffman was found on February 2 with a needle in his arm, and tests found heroin in samples from at least 50 packets in his Manhattan apartment.

The 46-year-old star of Capote and The Master said in interviews last year that he had sought treatment for a heroin problem after 23 years of sobriety.

PA Media