Police surrounded the Tree of Life synagogue after reports of an active shooter at the building in the city's Squirrel Hill neighbourhood, local TV news images showed.
Bowers also appeared to post two cryptic warnings about the shooting hours before the attack.
A suspect is in custody and "multiple" people dead following a shooting at a synagogue in Pittsburgh, Pennsylvania.
The synagogue is located at the intersection of Wilkins and Shady avenues.
The Tree of Life synagogue describes itself on its website as a conservative congregation that is traditional, progressive and egalitarian. People in Squirrel Hill area should remain sheltered. He exchanged gunfire with officers while confined on the third floor of the synagogue before being taken into custody.
Jonathan A. Greenblatt, chief executive of the Anti-Defamation League, said on Twitter that he was "devastated" by the shooting. I can't site by and watch my people get slaughtered.
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Mr Finkelstein said local synagogues have done "lots of training on things like active shooters, and we've looked at hardening facilities as much as possible". If they had protection inside the results would have been far better. Sam Schachner, president of Tree of Life, said in a phone call he had no comment at this time.
Stephen Weiss, a resident of the Squirrel Hill neighborhood who was present inside the synagogue, told the Pittsburgh Post-Gazette that the shooting "sounded like a loud crash in the hallway". As many as 100 people in total had gathered across the three congregations for a Sabbath service and a Bris ceremony.
President Donald Trump told reporters at Joint Base Andrews, Md., he would make a full statement about the attack during his afternoon speech in Indianapolis to the Future Farmers of America. In a tweet, Trump encouraged people to shelter in place and said "looks like multiple fatalities".
"This is an absolutely tragedy", Wolf said in another tweet.
" These senseless acts of violence are not who we are as Americans", he tweeted.
Police said there were multiple casualties. "I am sure that the law enforcement agencies and the legal authorities in the United States will investigate this horrific event thoroughly and that justice will be served on the despicable murderer".