Lincolnshire Police are searching for three youths who were seen with what appeared to be a gun.
Just before midday on Tuesday, August 11, they were called to the Tower Drive area of Lincoln.
The reports said three youths were there, with one of them holding what may have been a firearm.
Police said: “Although this report is unconfirmed, armed officers were deployed, and the NPAS helicopter has been used as part of our response.
“There will be a continuing police presence in the area as we continue to investigate this incident.”
There were unconfirmed reports suggesting the incident involved a Lincoln Prison inmate who escaped from Lincoln County Hospital care — but this is false, police said.
Many police vehicles patrolled the area around Arboretum park and Monks Road / Greetwell Road, and now the search appears to be heading towards Greetwell Quarry.
Anyone with information should call 101, quoting Incident 178 of August 11.