The shooter surrendered to Pittsburgh police and was being transported to Mercy Hospital, said Curt Conrad, chief of staff for City Councilman Corey O'Connor.
Another law enforcement official told CNN at least 12 people have been shot. Three police officers were shot, officials said earlier at an impromptu press conference. It's unclear if they are part of those casualties.
The shooter made anti-Jewish comments during the incident, a law enforcement official told CNN.
Pittsburgh police Cmdr. Jason Lando previously said there were "multiple casualties." Officers were dispatched to the scene after receiving reports of active gunfire at the synagogue, he said.
"It is imperative that the neighbors in the community surrounding the Tree of Life synagogue stay in their houses and shelter in place," Lando said. "Do not come out of your home right now. It is not safe."
Fred Rabner, a member of the synagogue, said it was a "close-knit community," and that everyone was calling around to make sure their loved ones are OK.
"Everyone is just shaken up and upset," Rabner said. "It's awful, it's just awful."