HARRIS COUNTY, Texas -

Authorities are looking for three men who they say held the customers and employees at gunpoint at a northwest Harris County restaurant.

It happened at around 3:30 a.m. Thursday when the men walked into a Denny's on Highway 290.

Authorities say when a clerk was not able to open the safe, one of the men hit her over the head with a gun.

The men took cash from a register and then ran off.

The employee was not taken to the hospital, but said she would go see personal doctor.

Not far away, on Highway 249 in northwest Harris County, there was another robbery about 30 minutes later at a Stripes convenience store. Harris County sheriff's deputies say the two cases could be related.

They said three masked men, two with guns, ran into the store, jumped over the counter and told an employee "I'm going to shoot her if you don't give me all of the money." 

Deputies say the three stole the money from the register and took off. Investigators say one robber fired his gun twice as he left. No one was hurt.