A post-mortem examination of a man found on a Timaru street early on Friday will help determine whether the police investigation is upgraded to a homicide inquiry.

Emergency services were called to York St in suburban Seaview about 4am after a man believed to be in his mid to late 20s was found lying on the road.

Attempts to revive him were unsuccessful.

Inspector Dave Gaskin says police hope to remove the body late on Friday and take it to Christchurch for the post-mortem examination.

He says the death was being treated as suspicious as they didn't know how he died.