LOS ANGELES, Feb. 1 (Xinhua) -- A middle school classroom shooting here which critically injured a teen and wounded four others was accidental, local police said Thursday.

A 12-year-old girl, who was suspected of opening fire, was taken into police custody and booked on a charge of negligent discharge of a firearm, according to Spokesman Josh Rubenstein of the Los Angeles Police Department (LAPD).

Anxiously waiting parents have reunited with their children after staff members walked the students out one at a time, following the shooting that occurred in a classroom at Salvador B. Castro Middle School in downtown Los Angeles on Thursday.

A 15-year-old boy who had been shot in the head was taken to Los Angeles County-USC Medical Center. There is so far no immediate threat to his life, doctors said at a news conference.

A 15-year-old girl who had suffered a gunshot injury to the wrist was in stable condition, according to the LAPD. Three other people, including two children and a 30-year-old woman, suffered minor injuries that were not caused directly by the shooting.

Police recovered a gun after the shooting. It still remains unknown how the gun was brought to school and how it went off in the classroom.

Following the shooting, the middle school and a nearby high school were placed on lockdown. Salvador Castro Middle School has a total enrollment of 428 students and 22 full-time teachers. More than 92 percent of the students are Hispanic, according the data on the website of the www.localschooldirectory.com.

In Los Angeles, students at middle and high schools are required to go through daily random searches for weapons. The daily search is normally done at different hours of the school day.

However, local media pointed out that relevant officials have not mentioned whether students at Salvador B. Castro Middle School were checked on Thursday.

The classroom shooting is the latest U.S. gun violence at schools, following a high school shooting in the U.S. state of Kentucky on January 23. A 15-year-old male student opened fire at Marshall County High in Kentucky, killing two students and injuring 18 others.

(Gao Shan in Los Angeles contributed to the report.)