HOUSTON -- A gun battle broke out between robbery suspects and a Houston police officer at an east Houston adult video store Friday, KPRC Local 2 reported.

Police said it started about 2:40 a.m. when at least three masked men robbed the Northshore Video and Smoke, a business opened 24 hours, located at 12915 East Freeway.

They were surprised when a Houston police officer showed up on the scene and one of the robbers opened fire on the officer, according to authorities.

The officer then fired back, striking the gunman in the head, police said. The wounded man was taken to Ben Taub Hospital where his condition was not released.

The other robbery suspects escaped on foot and in a pickup truck.

Investigators said the robbers were armed with shotguns and a pistol.

HPD said the officer was also armed with a shotgun.

Not all Houston police officers carry shotguns. It requires additional training that some say is worth it.

"One -- you have the intimidation factor. It's a lot more intimidating than a pistol. Also, you have better protection as an officer because, as you can imagine, with a pistol, you have one bullet, you have a very confined area that you need to focus on, whereas, if you're engaging multiple suspects, and there's some distance between you and the suspects, the shotgun does provide a bigger pattern and a better possibility of actually striking your target," said Capt. Dwayne Ready with the Houston Police Department.

As is standard procedure, the Houston Police Department will conduct an internal investigation into the shooting.

The officer, who was not injured, is a 16-year veteran with HPD.