Police evacuated a charity shop and cordoned off the surrounding area after a man donated a package marked "Do Not Open – Bomb".
A man in his 30s walked into the Derbyshire, Leicestershire & Rutland Air Ambulance charity shop in Oadby, Leicestershire, on Tuesday with several large cardboard boxes, one of which was sealed and marked with the bomb warning, a statement from the charity said.
When the shop manager, Louise Kenyon, noticed the message, she called 999 and police advised her to evacuate the store immediately, according to the statement. The donor soon returned with more boxes but was unable to deliver them because the store was closed, so he left them on the pavement outside.
The charity said the area around the shop was cordoned off and police investigated the package with specialist units, including a sniffer dog. Police said "nothing untoward was found" and a man was arrested at the scene. He was later released without charge.
Andy Williamson, chief executive of DLRAA and sister service Warwickshire & Northamptonshire Air Ambulance, said: "Whether a hoax or a genuine threat, it is abhorrent that someone would target our life-saving charity in this manner.
"The air ambulance exists to prevent loss of life and serve the local community, and we are shocked to have been at the centre of such an incident."
A spokeswoman for Leicestershire Constabulary confirmed that police were called to a report of a suspicious package in Oadby on Tuesday afternoon.
"Following enquiries, nothing untoward was found," she said. "One person was arrested at the time but he has since been released with no further action. As a precautionary measure we did cordon off the area around the incident."