Deliberate contamination of food intended for patients at one of Adelaide's biggest hospitals is being investigated by police, with testing underway to determine whether faeces was the substance involved.

Key points: Jellies and custards at Flinders Medical Centre were contaminated with a "solid organic" product

Jellies and custards at Flinders Medical Centre were contaminated with a "solid organic" product Police would not rule out faeces, and said the material was being analysed

Police would not rule out faeces, and said the material was being analysed Health staff are assisting police with a criminal investigation

Police said it was too early to tell exactly what was used to contaminate the desserts at Flinders Medical Centre, which included jelly and custard.

"We are satisfied that there are no patients who have been fed the contaminated foodstuffs. No threat or claim has been made in connection with this," Acting Assistant Commissioner Joanne Shanahan said.

Asked whether it was faeces, and what colour the substance was, Assistant Commissioner Shanahan said she could not comment beyond saying the "matter was being forensically analysed".

The contaminated items were discovered yesterday on a refrigerator tray in a hospital kitchen, and police were notified this morning.

They have now launched a criminal investigation.

"During a routine food safety inspection yesterday a small number of desserts were identified as contaminated," said Sue O'Neill, the CEO of the Southern Adelaide Local Health Network.

"Staff were vigilant and isolated the area and raised the alarm. Management then initiated a small assessment team who investigated all other prepared food."

Ms O'Neill said the contaminant was a "solid, organic-looking product" and was "very obvious".

"There was an abnormal appearance," she said.

The hospital is helping police with the investigation, which involves going through CCTV.

Police said it was unclear if the contamination had occurred on site.

"We are looking at anyone who may have had access into this area of the hospital," Assistant Commissioner Shanahan said.

Police asked anyone with information to call Crime Stoppers on 1800 333 000.

Last month, the ABC revealed a gastro outbreak was affecting patients and staff at the hospital.