The incident took place around 8 p.m. local time and the first shots were fired in the proximity of the synagogue, a spokesman for the Ministry of the Interior told ABC News. The gunmen then allegedly opened fire in five other places in the downtown area around the city, the spokesman said.
Seven of those injured were listed in critical condition as of Monday evening and were receiving treatment at six area hospitals, Christoph Mierau of the Vienna Health System confirmed to ABC News.
The assault was carried out by at least one gunman who was shot and killed by officers. The suspect was armed with an assault rifle, among other handguns, and was appearing to wear an explosive vest which turned out to be a dummy. The suspect's apartment has also been opened by a SWAT team and searched.
Locals are being advised to avoid nearby public places and public transportation by authorities who said initially they were responding to "several suspects armed with rifles" at "six different shooting locations." The scene was considered "still active" late Monday, police said via Twitter.
The head of the Jewish community in Vienna, Oskar Deutsch, told The Associated Press earlier in the day that the shooting was near the city's main synagogue, but it wasn't clear whether the building was targeted. It was closed at the time of the incident.
"We are currently experiencing difficult hours in our republic. I would like to thank all the emergency services who are risking their lives, especially today, for our safety. Our police will take decisive action against the perpetrators of this vile terrorist attack," Austrian Chancellor Sebastian Kurz said via Twitter. "I am glad that our police officers have already been able to neutralize a perpetrator. We will never allow ourselves to be intimidated by terrorism and will fight these attacks resolutely by all means."
The Ministry of the Interior spokesman said the manhunt was still ongoing as of midnight local time.
Children have been encouraged not to attend classes Tuesday, even though schools are not closed.
Security checks -- such as authorities stopping random cars and checking them -- at the border have been launched, in response to the attack, according to to David Schoen, a spokesman for the Czech police.
The U.S. embassy in Vienna also warned Americans in the city to be cautious and stay indoors as the manhunt continues.
All Synagogues, kosher restaurants and Jewish supermarkets are set to stay closed today across Austria on Tuesday.
There will be a police press conference at 2 p.m. local (8 a.m. EST) where further details about the attack will be given.