Police and the RSPCA are investigating allegations a duckling rescue attempt in a Launceston car park ended in a bird's decapitation at a nearby restaurant.

In a Facebook post, Launceston woman Adina Purton said she and a friend were trying to rescue some ducklings that were wandering around a car park on Saturday night.

Ms Purton said the animals were frightened by cars and took refuge in the storeroom of a restaurant.

"It was then that [a man] came out and told us that one of the ducklings had been found dead on the floor," the post said.

"We asked if we could see the body of the duckling so that we knew it had not been hurt or cruelly mistreated.

"We were then handed a box which contained a small, headless baby duckling."

The restaurant's Facebook page was flooded with complaints and comments, and has since been taken down.

Ms Purton's post had been shared more than 2,000 times by Sunday and had generated more than 1,000 comments.

Tasmania Police confirmed they had responded to reports of the mistreatment of an animal at the restaurant.

In a statement, it said a deceased duckling was located but that there was no evidence to suggest it had been deliberately injured.

The RSPCA confirmed it was also investigating the incident.

"There has been one [complaint] come through ... and that has information with it that will be useful to us," RSPCA Tasmania chief executive Peter West said.

"We'll have a look at the case, we'll talk to police and we'll see how best to address the situation on Monday."