An eighth-grade boy at a Hempstead middle school was stabbed in the head minutes after he left school Thursday.

According to Nassau police, the 13-year-old victim is in critical condition at Winthrop University Hospital. Police say dozens of fellow students witnessed the altercation as they left around noon. Alverta B. Gray Schultz Middle School had a half-day due to parent-teacher conferences. One witness says the stabbing began as a street fight and believes the assailant, who remains on the loose, is also a student.

Police ask anyone with information about the incident to call Nassau Crime Stoppers at 1-800-244-TIPS. Investigators remind the public that all calls remain anonymous, and they are offering a reward for information leading to an arrest.