Authorities are investigating an armed robbery at a north Houston gas station.

It happened at the Exxon gas station on the North Freeway at Tidwell around 6 a.m. Tuesday.

Houston police said two masked men walked into the gas station, held the clerk at gunpoint and demanded money.

Police said the robbers got away with about $500.

The clerk was not injured.

Houston police are reviewing surveillance video to learn more about the robbery.