Pittsburgh police told the Pittsburgh Post-Gazette the incident began about 5:30 p.m. when the suspect allegedly cut another man's face at the intersection of Penn Avenue and Penn Circle and then ran inside the nearby Target store.
Police spokeswoman Diane Richard said store security told police two men followed the knife-wielding man into the store, but the man chased one of them out of a restroom and "ran toward the checkout lanes and grabbed a 16-year-old female who was standing with family members and held her in front of him with knife still in hand."
Richard said the girl was cut in the back and arm and was hospitalized in serious condition.
She said one man was cut on the lip and another sustained deep cuts to his fingers. A bystander was taken to a hospital for chest pain.
Officers then used a stun gun and pepper spray to subdue the attacker. He was being treated before being taken to the Allegheny County Jail. Charges were pending, police said.
An officer was treated for exposure to pepper spray.
"None of the injuries reported appeared to be life-threatening," Richard said.
The names of the injured and the suspect had not been released.
KDKA-TV, Pittsburgh, reported the suspect was armed with a long kitchen knife. The TV station said six people were injured, including four who suffered knife wounds.
Chris Jones, who was in the store at the time, told KDKA-TV he saw the suspect being beaten.
"He was getting his tail whooped with a bat, with fists," Jones said. "He was getting tore up and I think he deserved it."
Target said in a statement "the safety and security of our guests and team members is a top priority for Target and we are partnering closely with local law enforcement."