PORTLAND — Portland police are investigating an armed robbery that took place Thursday night at a TD Bank ATM on Union Street.

Lt. Jim Sweatt said a woman was beginning to make a transaction at the ATM when a man wearing a dark neoprene mask and a dark, gray hooded sweatshirt approached her and demanded she withdraw money for him.

The suspect, who was holding a handgun, fled on foot with an undisclosed amount of cash.

Portland police used a canine to track the suspect to Pleasant Street near the city’s West End but were unable to locate him.

Sweatt said the man is described as being about 6-foot-2, light-skinned and wearing jeans. His hooded sweatshirt was long, falling well below his waist.

The robbery took place around 5:30 p.m. The woman was shaken but not injured.