Police believe a serious assault has taken place behind a church in Hamilton.

Detective Sergeant Andrew Mortimore said they've discovered human blood behind the Activate Church in Bisley Road in the city's east.

He said they've established the blood was there at 11 yesterday morning when the facility was used by an external group for a function.

Detective Sergeant Mortimore said they haven't been able to identify any possible victims as yet.

They want to speak to anyone with information.