At Least 11 People Killed In Pittsburgh Synagogue Shooting

The US man suspected of killing 11 people at a synagogue in Pittsburgh has been charged with obstructing the exercise of religious beliefs resulting in death.

Federal prosecutors said Robert Bowers was charged on Saturday night in a 29-count criminal complaint.

The charges also include 11 counts of using a firearm to commit murder, weapons offences and charges alleging Bowers seriously injured police officers while obstructing the exercise of religious beliefs.

Authorities said six people, including four police officers, were also wounded during Saturday's shooting at the Tree of Life Congregation in Pittsburgh's Squirrel Hill neighbourhood.

Law enforcement officers at the scene where multiple people were shot in Pittsburgh's Squirrel Hill neighbourhood. Image: AAP

Prosecutors have scheduled a Sunday morning news conference to discuss the case.

Thousands of people jammed an intersection amid a light rain for a vigil on Saturday evening for the victims of the mass shooting.

The gathering included prayers and singing in memory of those killed and wounded.

A "vote, vote, vote" chant broke out during the emotional gathering where some derided the nation's political climate.

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People gather for a vigil in the aftermath of a deadly shooting at the Tree of Life Congregation. Image: AAP

Several attendees blamed the shooting on the nation's political climate and said they took little solace in a planned visit by President Donald Trump.

Democratic Governor Tom Wolf attended the vigil, suspending a campaign bus trip after learning of the attack.

Earlier, Scott Brady, the US Attorney for western Pennsylvania, described the suspected gunman's actions as representing "the worst of humanity".

"We are dedicating the entire resources of my office to this federal hate crime investigation and prosecution," he said.

Thousands gathered to mourn the 11 victims who were killed. Image: AAP

FBI special agent Bob Jones said the Federal Bureau of Investigation, which is leading the probe into the attack, believed Bowers was acting alone, adding: "We have no knowledge that he was known to law enforcement before today."

KDKA television cited police sources as saying Bowers walked into the building and yelled "All Jews must die".

Bowers was in a hospital in fair condition with multiple gunshot wounds.

Patients at area hospitals included a 61-year-old woman, a 70-year-old man, and a 55-year-old officer. No children were killed, authorities said.

People embrace following the fatal shooting. Image: AAP

A social media post by Bowers on Saturday morning said a Jewish refugee organisation, the Hebrew Immigrant Aid Society, "likes to bring invaders in that kill our people. I can't sit by and watch my people get slaughtered. Screw your optics, I'm going in."

The comment was posted on Gab, a Philadelphia, Pennsylvania-based social networking service created as an alternative to Twitter. In a statement, Gab.com confirmed the profile belonged to Bowers and also said it had suspended the account and contacted the FBI about it.

The shooting, for which Bowers had an assault rifle and three handguns according to the FBI's Jones, prompted security alerts at houses of worship around the country.

It follows a spate of pipe bombs found mailed in recent days to prominent political figures, mostly Democrats including former President Barack Obama.

The Tree of Life synagogue in the city's Squirrel Hill neighbourhood, a heavily Jewish area, was holding a Shabbat religious service at the time of the shooting.

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Police are normally only present at the synagogue for security on high holidays, Michael Eisenberg, former president of the synagogue, told KDKA.

"On a day like today, the door is open, it's a religious service, you can walk in and out," he said.

Around the time, three congregations amounting to about 100 people would have been using the building, Eisenberg said.

Shortly after reports of the shooting emerged, US President Donald Trump said in a tweet he was watching what he described as a "devastating" situation.

Trump told reporters later that the killings might have been prevented if there had been an armed guard in the building.

"If they had some kind of a protection inside the temple maybe it could have been a much more different situation, they didn't," he said when asked about a possible link to U.S. gun laws.

CEO of the Anti-Defamation League Jonathan Greenblatt said it is "likely the deadliest attack on the Jewish community in the history of the United States".