Auckland police are investigating the death of a young man in suspicious circumstances.

The 21-year-old local man had been with a group of young people in a park in Otahuhu, about 5.30am on Saturday, police spokeswoman Ana-Mari Gates-Bowey told NZ Newswire.

There had been an argument, but did not appear to be any fighting, when the man collapsed and died.

The group had been drinking all night, Miss Gates-Bowey said.

Police had spoken to the group and an older couple, who were part of a church group, who witnessed what happened.

Police were examining the scene and hoped a post mortem on Sunday would reveal how he died.