The previous three shootings each involved a fatality. At least one student was critically wounded at the bus stop, a 16-year-old who was hit nine times, Kevin Bethel, the city’s police commissioner, said at a news conference. The others were in stable condition.

Bethel said the Northeast High School students, ranging in age from 15 to 17, were waiting for the bus around 3 p.m. when three people emerged from the car, which was waiting at the scene, and fired more than 30 shots.

Police then received numerous 911 calls about a “mass shooting on the highway near Dunkin’ Donuts,” in northeast Philadelphia, according to police spokesperson Tanya Little.

The injured teens were taken to Einstein Medical Center and Jefferson Torresdale Hospital, according to John Golden, a spokesperson for the Southeastern Pennsylvania Transportation Authority, or SEPTA. Two buses — a Route 18 bus and a Route 67 bus — were hit by gunfire, but there were no reports of injuries to passengers or the driver.

Superintendent Tony Watlington Sr. said officials were “absolutely heartbroken and angry that innocent children walking home from school would be impacted by gun violence, and we agree with the mayor: Enough is enough.”

The scene was cordoned off with yellow police tape in the aftermath of the shooting, with dozens of evidence markers lying on the rain-slicked pavement.

Neighborhood resident Jessica Healy, who was with her 2-year-old daughter, said the area has become more unsafe in recent years, and she has neighbors who are already in the process of moving due to previous incidents.

“I think it’s really sad and just dangerous that I don’t even want to walk my daughter out here,” Healy said.

Another longtime resident, Brenda Keith, said she doesn’t take extraordinary measures to stay safe, other than being aware of her surroundings in case she suddenly needs to get away from trouble. She understands if people don’t feel safe in the city right now or are uneasy about riding SEPTA, but she’s determined not to let shootings stop her from living her life.

“But we’re not the only city that’s going through this. a€? I’ve been here a long time and things have gotten worse, but that’s the way life is,” Keith said.

Wednesday’s shooting followed shootings the previous three days in which someone was killed while riding, entering or leaving a SEPTA bus.

Tuesday’s shooting occurred around 6:35 p.m., when police said a verbal argument and then a physical fight began. One of the two passengers exited, turned and fired two shots from a 9 mm handgun, hitting a man later identified as 37-year-old Carmelo Drayton. He died shortly afterward at a hospital.

The shooter, who officials said was wearing one of the kinds of masks not allowed on the transit system, fled. Authorities were investigating possible motive, and no other injuries were reported.

SEPTA’s chief of transit police, Charles Lawson, said the shots were fired at the victim while the driver was “immediately behind.”

On Monday, a 17-year-old student was killed and four other people were wounded when gunfire erupted at a bus stop. The victims included two women who were riding on a bus.

And on Sunday, around 11:30 p.m., a 27-year-old man was killed by another passenger moments after they both got off a bus. Witnesses said the two had argued, but a motive remains under investigation.

No arrests have been made in any of the shootings, Frank Vanore, deputy commissioner of the Philadelphia police department, said Wednesday.

While serious crime overall is down along the transportation system, Lawson said, a pattern that has emerged over the past year and a half is people carrying weapons, usually illegally, getting into an argument and then opening fire. He vowed that officials would enforce crime aggressively and unapologetically and use “every legal means at our disposal to target illegal gun possession.”

“We’re going to target individuals concealing their identity. We’re going to target fare evasion. We’re going to target open drug use,” Lawson said. “We’re going to target every criminal code on the books.”

Officials are increasing monitoring of security cameras and looking into ways to let employees report potential problems discreetly and safely, Lawson added.