The gunman reportedly walked in about 5 a.m. at 250 Gateway Blvd. and pointed a black, semi-automatic handgun at the clerk, authorities said. He demanded that the clerk hand over the register's contents and took off on foot with an undisclosed amount of money.

The suspect is described as a black male of an unknown age, standing 6 feet tall with a slender build. He was wearing a black hooded sweatshirt and bluejeans, along with a black ski mask.

Anyone with information about the suspect or robbery is asked to contact South San Francisco police at 650-877-8900 or the Anonymous Tip Line at 650-952-2244. The investigation is ongoing.

Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.