The incident unfolded before 6 pm when the suspect's car rammed another vehicle (Representational)

Texas authorities on Friday were searching for a gunman who shot and killed two men on a Houston freeway on Thursday before being chased off by a witness who opened fire at him.

Authorities on Friday described the gunman as a Hispanic male in his 20's armed with what they believe was gun similar to an AR-15 assault-style weapon.

Police could not confirm whether the victims were targeted or whether the incident was a case of road rage.

Houston Police Chief Bobby Dobbins said the killings could also have been drug-related, as narcotics were found in the targeted car.

"As crazy as things are right now in our society, was this a road rage incident and these guys just happened to have narcotics in the car?" Dobbins told reporters.

The incident unfolded just before 6 p.m. when a car driven by the suspect rammed another vehicle on Interstate 10 in Houston. The suspect then stepped out of his car, described by police on Friday as a "newer model, dark colored four-door sedan," and began shooting at the front of the struck vehicle, Dobbins said.

There were two people inside the targeted car.

An unidentified male witness pulled out a pistol and started firing shots at the suspect, Dobbins said. The suspect then fled in his vehicle, along with a male passenger.

Other witnesses tried performing CPR on the two victims, aged 25 and 33, before authorities arrived, but to no avail.