Two people were shot and two others injured when a student got into a fight and drew a gun in a classroom at a Texas high school on Wednesday, police said.

Arlington assistant police chief Kevin Kolbye said police were searching for an 18-year-old student at Timberview High School in Arlington, identified as Timothy George Simpkins, who fled after the shooting.

"This is not a random act of violence," Kolbye told reporters. 

"A student got into a fight and drew a weapon."

He said three people were hospitalized, two of them with gunshot wounds. 

A fourth person, a pregnant woman, was treated on the scene for minor injuries and released.

Kolbye said more than "two or three shots" were fired during the incident.

The school was locked down following the shooting and Arlington police set up a secure area for parents to reunite with their children.

Live television images showed a heavy police presence around the school, with armed officers searching the sprawling campus and ambulances and fire trucks on the scene.

A fleet of yellow school buses could be seen preparing to evacuate students from the school.

Timberview High School has an enrollment of around 1,900 students.

After a year spent largely learning online, US schools have returned to the classroom, reviving the fear of on-campus shootings, with multiple small-scale incidents reported in recent weeks.

More than 248,000 students have been exposed to gun violence in US schools since 13 people were killed in the massacre at Columbine High School in Colorado in 1999, according to data compiled by The Washington Post.

The figure includes those caught up in the violence, such as witnesses, and those forced to evacuate educational institutions when gunfire erupted.

In 2018, there were 25 school shootings and 23 more in 2019.

The deadliest recent school shooting in the United States took place in 2018, when 17 people were killed in a shooting by a former student at a high school in Parkland, Florida.