Multiple students were wounded, one critically, in an after-school shooting at a San Francisco high school parking lot in the Excelsior District on Tuesday afternoon, according to reports. A female student was critically wounded, while two male students suffered non-life-threatening injuries.

The San Francisco Examiner reported a fourth victim walked into San Francisco General Hospital with injuries.

The incident occurred at about 3:15 p.m. local time at June Jordan School for Equity. The school immediately went on a lock out, but it was lifted by police at 4:03 p.m., according to the school district.

Four men believed to be suspects were seen running down a nearby street and remain at large.

A mother who was picking up her child told CBS News that she heard six shots fired.

“This was an isolated incident outside of the school building where one student was being targeted by outsiders. Wellness staff is at the school to support students," the San Francisco Unified Public School District said in a statement.

In May, one student was fatally shot and another was shot and stabbed near Novato High School, about 20 miles north of San Francisco.