Video posted to Snapchat shows a group of teenage boys punching and spraying water on an 11-year-old girl in Brooklyn — and police are investigating the incident, authorities said.

The girl was walking with a friend at about 8 p.m. Dec. 18 near Nostrand Avenue and Avenue Y when the group of teens attacked her, cops said.

One of the bullies threw a backpack at her, while the other sprayed her in the face with water and chucked a bottle at her, the video shows. Both of the suspects then punched her in the head several times.

Her friend recorded the assault and later posted it to Snapchat, authorities said.

Police are searching for the suspects, who ran off after the attack, cops said.

The girl suffered minor injuries, authorities said.