The Lincs and Notts air ambulance landed in Dysart Park in Grantham yesterday afternoon after reports of a boy falling from a tree.
Pictures of the air ambulance were put on Facebook by Tracy Burling just after 6.30pm.
She said the helicopter later took off and left a land ambulance crew to deal with the casualty.
A spokesman for Lincs & Notts Air Ambulance said: “We received a call at 17:57 to Dysart Park in Grantham. The caller reported a patient who had fallen. We sent a paramedic on a car and the Nottinghamshire and Lincolnshire Air Ambulance. One patient was taken to Lincoln County Hospital for further care.”