A girl believed to be 12 years old opened fire Thursday in a middle school classroom, critically wounding one classmate and injuring three others, authorities said.

Police arrested the girl and recovered a gun after the shooting that happened just before 9 a.m. at Salvador B. Castro Middle School near downtown, said Steve Zipperman, chief of the Los Angeles Unified School District police force. A possible motive was not identified as the investigation was in its early stages.

News footage showed a dark-haired girl in a sweatshirt being led from the school in handcuffs as anxious parents and family members gathered on a street corner, talking on their phones and awaiting word about their children.

Diego Salinas had just dropped his 12-year-old sister at the school and was stunned when she called minutes later to say there had been a shooting.

“There were so many things crossing my mind,” said Salinas, who was still shaking hours later. “I wanted to cry. I wanted to scream. I wanted to run. I wanted do so many things.”

Claudia Anzueto said her 12-year-old son was crying when he called her from a borrowed cellphone. He said he heard a gunshot in the next classroom and knew the suspect.

“Not safe, very insecure,” said Anzueto, who said there were no metal detectors at the school. “I fear for my son’s life. You know what I mean, you really hear about things like this in the news, and just to hear that something like that happened so close to home, it scared the life out of me.”

The district has a policy requiring every middle and high school campus to conduct daily random searches by metal-detector wands at different hours of the school day for students in the sixth grade and up.

Student Melanie Valencia, 13, said the school did a random security search Thursday, but she’s never been searched.

“It’s crazy because I don’t know how she got the gun,” she said.

The most seriously injured victim, a 15-year-old boy shot in the head, was taken to Los Angeles County-USC Medical Center and remained in intensive care during the afternoon but was doing well.

“This child was extremely lucky,” said Dr. Aaron Strumwasser, a trauma surgeon. “The trajectory of the bullet did not hit any vital structures that were an immediate threat to life.”

A 15-year-old girl with a gunshot wound to the wrist was hospitalized in fair condition. An 11-year-old boy and a 12-year-old girl were grazed and were treated and released from the hospital. A 30-year-old woman who was treated after the shooting was not hospitalized and the nature of her injury was not immediately known.

The school’s campus was placed on lockdown but most classes continued. The school has about 365 students in grades 6-8 and almost all are Hispanic and many are from low-income families.

“We will attend to the needs of these students who witnessed this very carefully, with the understanding this is very traumatic,” Zipperman said. “We have our school mental health folks that are here to support the needs of the students.”

At the end of the school day, children were escorted individually out of the school. Many were crying as they were embraced by emotional parents.

-AP