BREAKING: Fist Fight Leads To School Shooting In Arlington, Several Shot

ARLINGTON, Texas -- Four people were injured after a gunman opened fire at a Dallas-area high school on Wednesday.

Three of those four people were taken to the hospital. The nature of their injuries is not clear.

Authorities believe an active shooter opened fire at a Texas high school and shot "multiple persons" Wednesday, according to a preliminary internal police briefing.

Law enforcement agencies responded to an "active shooter situation" at Timberview High School in Arlington, a city west of Dallas. Local news reports show heavily armed police and other emergency responders in the school's parking lot.

The "unknown suspect" immediately fled the scene after opening fire, according to that preliminary briefing. The number of victims and their conditions is unknown.

Speaking to ABC News, a teacher at the school said he heard the shooting from inside his classroom. He and his students created a makeshift barricade in front of their door with classroom furniture and are currently sheltering in place.

Police said the scene at the high school is currently secure, and there is no current threat to the public or the school.

The school was on lockdown but Mansfield Independent School District has begun the reunification process for those students and families. Students are being safely escorted on buses.

The police department said on Twitter that officers were doing a "methodical search" and were working closely with other law enforcement agencies.

Two videos were uploaded to social media from the school, the first one showing two teens in a scuffle during class and the second showing classmates run from their desks as shots rang out.

We will keep you updated as information comes in.