Police tape marks the scene outside a Twin Peaks restaurant in Texas.

A gunman hijacked a US postal truck and opened fire at random in the US state of Texas on Saturday, shooting dead at least five people and wounding many others before dying in a shootout with officers.

Police identified the suspect as a white man in his mid-30s, but could not yet name him or say why he carried out the attack in the West Texas cities of Midland and Odessa.

A police car is parked outside The Medical Center Hospital where victims of a mass shooting are being treated. AFP

Coming less than a month after a gunman killed 22 people in the Texas city of El Paso, the latest bloodshed immediately ignited fresh calls for gun control to stem the US scourge of mass shootings.

"We have at least 21 victims, 21 shooting victims and at least five deceased at this point in time," Odessa city Police Chief Michael Gerke told reporters.

Three police officers were injured, he said.

A rifle through the window

Troopers had initially tried to pull over a passenger vehicle on the Interstate 20 highway but before it stopped, "the male driver (and only occupant in the vehicle) pointed a rifle toward the rear window of his car and fired several shots toward the DPS patrol unit," the Texas Department of Public Safety said in a statement.

One trooper was wounded, the suspect fled the scene, "and continued shooting innocent people," the department said.

Police tape marks the scene outside a Twin Peaks restaurant after multiple people were shot in Odessa, Texas. AFP

Some of the shots were fired on the highway linking the cities of Odessa and Midland, where cars were left with bullet holes.

During his rampage, the suspect had switched vehicles by hijacking the postal van, and Gerke said he "would assume" the postal worker was among the victims.

Police said the suspect died during an exchange of fire with law enforcement at a movie theater in Odessa.

Alex Woods, a witness, told CNN that near the movie theater "I could see a bunch of gunfire going off. And I could see the officer walking up to the mail van and discharging his weapon into it.

Agence France-Presse