A New York Police Department spokesman confirmed the four people were taken into custody from an address in the city.

The spokesman declined to confirm the arrests were related to Hoffman's death.

But news reports in the US say the arrests have been made in relation to substances seized from the actor's Manhattan apartment.

Mourners leave flower's outside Hoffman's apartment

Hoffman, 46, was found dead at his home on Sunday morning with what officials said was a needle in his arm.

Police sources said around 50 envelopes - some empty, some unopened - were discovered inside the apartment and that tests showed they contained heroin.

The samples tested negative for the powerful additive fentanyl -  a synthetic morphine which is added to intensify the high and has been linked to 22 suspected overdose deaths in western Pennsylvania.

Hoffman spoke openly of his battle with drugs when he was a younger man, but after 23 years sober he admitted in interviews to renewed substance abuse problems.

The actor's family has described his death as "tragic and sudden".