Update, 10/6/2021, 3:16 p.m. ET:
The Dallas Morning News reports that authorities were able to take the suspect into custody.
He faces three charges of aggravated assault with a deadly weapon.
CNN reports that Arlington Police Department Assistant Police Chief Kevin Kolbye said, "He is currently in the police station at Ott Cribbs in Arlington, Texas. And detectives are talking to him at this point in time."
One victim, a male student, underwent surgery and is recovering.
A second victim — an adult male — is not in surgery but is in a "good position."
A third person who was injured is expected to be released from the hospital soon.
Update, 10/6/2021, 1:02 p.m. ET:
Officers already inside the school at the time of the shooting were reportedly able to provide support.
Arlington Police Department Assistant Police Chief Kevin Kolbye said that two police officers from the Mansfield Independent School District were inside the school at the time of the shooting and were able to administer aid immediately following the incident.
"Kolbye said he believed three of those injured during today's incident were students and one was a person who may be a teacher, but he could not confirm those details during a news conference," CNN reported. "He did say a pregnant woman fell during the shooting and was treated at the scene but was not transported to the hospital."
Update, 10/6/2021, 12:48 p.m. ET:
Jeff Boshek, special agent in charge for the Bureau of Alcohol, Tobacco, Firearms, and Explosives' Dallas Field Division, said that the agency will track down the weapon used by the suspect.
"We'll figure out where this individual got this gun from," he vowed during a press conference on the incident. "Our agents won't sleep, working with our partners here, to figure out how he got this weapon in his hand to come in this school and cause this tragedy today. So, I don't have much information I can give you on the weapon. Obviously, we don't have that yet. We haven't been in the school to figure out the caliber of the weapon or anything like that yet, but as soon as we do, we'll have something to get out to you guys."
Update, 10/6/2021, 12:22 p.m. ET:
Police say that they believe the shooting took place following a fight "between a student and another individual in a class."
At the time of this reporting, police say that there are four victims.
The suspect is 18-year-old black male Timothy George Simpkins, who is on the loose and is considered armed and dangerous. He is believed to be driving a 2018 Silver Dodge Charger with license plate PFY-6260.
The Arlington Police tweeted, "We are looking for a shooting suspect in today's incident at @mansfieldisd Timberview School. Please call 911 if you know the whereabouts of 18-year-old Timothy George Simpkins who may be driving at 2018 Silver Dodge Charger with license plate PFY-6260."
Update, 10/6/2021, 12:14 p.m. ET: KTVT-TV reports that the "all clear" has been given at Timberview High School in Arlington, Texas, on Wednesday after an active shooter situation unfolded.
The Mansfield Independent School District has begun the reunification process families, and officials said that students are "safely" being escorted to buses.
One mother told KTVT reporter Nicole Jacobs that her child was able to get into contact with her during the incident as police searched the hallways for the suspect.
"I haven't been able to reach my son for 20 minutes," the unnamed parent said. "When we last spoke, I heard the other kids crying and screaming in the classroom."
The station reported that officials with the Arlington Police Department confirmed that the ATF Dallas Field Division, Mansfield Police Department, Grand Prairie Police Department, and Mansfield ISD police are all working the scene and are executing a "methodical search" of the school campus.
Parents are being directed to the Center for Performing Arts to reunite with their children.
Original story continues below ...
Gunfire erupted at Timberview High School in Arlington, Texas, on Wednesday, reportedly killing at least one person at the time of this reporting and injuring multiple other people.
What are the details?
Police are responding to reports of an active shooter Wednesday morning at the Arlington school, according to various reports.
According to the Atlanta Journal-Constitution, police have confirmed "multiple victims" in the shooting as people were being transported to local hospitals following the apparent attack.
At least one other area school has been placed on lockdown, according to the report.
Video footage believed to have been taken inside the school as the gunshots rang out appeared on social media soon after reports of the shooting went live.
WYFF-TV reported that Arlington Mayor Jim Ross said that at least two people were injured, but said that the severity of injuries were unknown.
KXAS-TV reporter Maria Guerrero also reported that police were continuing to work to detain the suspect as of 10:45 a.m. local time.
The school remains on lockdown at the time of this reporting.
This is a breaking story and will be updated as events warrant.