Officers were called to Fountain Lane at about 6.20pm today.
A spokesman for the force said: “We have launched a murder investigation. The area has been cordoned off and we will be at the scene for the foreseeable future.
“The young girl’s parents have been informed and our thoughts are with them at this incredibly difficult time. Her family will be supported by specialist trained officers.”
Anyone with information in relation to the incident is asked to call Lincolnshire Police on 101 quoting incident number 419 of July 28 or contact the force via [email protected] (using incident number 419 of July 28 in the subject line).
Anyone wishing to remain anonymous, is asked to contact the independent charity CrimeStoppers on 0800 555 111 or online.