Two people including one attacker were killed and 15 others were injured in central Vienna on Monday evening in what Austrian Chancellor Sebastian Kurz described as a "repulsive terror attack."
A police officer is among the seriously injured, the Vienna Police (LPD Wien) wrote on Twitter.
There are six different shooting locations and the attackers used long guns, it added.
Several "heavily armed and dangerous" attackers were still on the loose as police shut down and sealed off large parts of central Vienna in a manhunt, Interior Minister Karl Nehammer said, adding the incident appeared to be a terrorist attack.
All six locations were in the immediate vicinity of the street housing the central synagogue, said Nehammer, adding that border checks are reinforced and children are not required to go to school on Tuesday.
First gunshots were fired at around 8:00 p.m. local time in the city's centrally-located first district. The shooting began just hours before Austria was to re-impose a coronavirus lockdown to try to slow the spread of COVID-19, and bars and restaurants played host to people enjoying a final night of relative freedom.
Jewish community leader Oskar Deutsch said on Twitter it was not clear whether the Vienna synagogue and adjoining offices had been the target and said they were closed at the time.
Nehammer urged Vienna residents to remain in their homes and keep away from all public places or public transport.
Frequent sirens and helicopters could be heard in the city center as emergency services responded to the attack.
Austrian Chancellor Sebastian Kurz condemned the "hideous terrorist attack" in the Austrian capital, vowing to "take decisive action" against the perpetrators.
"We are currently going through difficult times in our republic," Kurz wrote on Twitter. "We will never allow ourselves to be intimidated by terrorism and will fight these attacks resolutely by all means."
EU leaders, countries condemn Vienna shootings
European Council President Charles Michel and European Commission President Ursula von der Leyen as well as leaders of European countries condemned the shooting attacks in Vienna late on Monday.
"Europe strongly condemns this cowardly act that violates life and our human values," said Michel on Twitter. "We stand with Austria," he stressed.
Von der Leyen said she was shocked and saddened by the brutal attack that took place in Vienna. "Europe stands in full solidarity with Austria. We are stronger than hatred and terror."
French President Emmanuel Macron said on Monday evening that the French share the shock and sorrow of the Austrian people following the shootings, pledging that "our enemies must know who they are dealing with. We will not give in."
The German Foreign Office tweeted late Monday, "Even we don't know the full extent of the terror yet, our thoughts are with the injured and victims at this difficult time. We will not give way to hatred which is aimed at dividing our societies."
In London, British Prime Minister Johnson said the "UK's thoughts are with the people of Austria – we stand united with you against terror."
Italian Prime Minister Giuseppe Conte tweeted: "There is no room for hatred and violence in our common European home."
Dutch Prime Minister Mark Rutte called the shooting "a heinous act" and expressed "solidarity" with Austria.
(With input from agencies)