The girl reportedly went swimming with her mother at around 2:00 pm before both of them began struggling when they suddenly found themselves in deep waters.
The woman managed to make it back to shore, but her daughter disappeared from sight and has not been seen since, according to Italian news agency ANSA.
Fire brigade divers and volunteers began desperately searching for the girl on Thursday afternoon, in the hope of finding her before nightfall.
No further updates have been made.
The incident happened off the beach at Ulisse Guzzi Park, near Lecco.
The family was visiting Lake Como from Monza, in Lombardy.
With ANSA
