Several people were likely killed, and a number of others had been wounded in central Vienna following exchanges of gunfire late on Monday, Austrian interior minister said.
Police said the attack in Vienna involved six crime scenes and at least one police officer was among the 15 wounded. Police had shot dead one perpetrator, police said on Twitter.
Interior Minister Karl Nehammer told ORF the incident is believed to be terror attack. "At the moment I can confirm we believe this is an apparent terror attack," he said. "We believe there are several perpetrators. Unfortunately there are also several injured, probably also dead."
The Austria Press Agency quoted Nehammer's office as saying that one attacker was killed and another could be on the run.
Vienna police urged people to avoid all open spaces and public transport in the city. Police said trams and buses weren't stopping and urged social media users not to post videos of the ongoing police operation, so as not to endanger officers.
"There are several injured persons," police tweeted. "We are on site with all available forces. Please avoid all public squares in the city."
Newspaper Kronen Zeitung reported that an officer guarding the city's central synagogue was among the injured. The synagogue has police officers stationed near the entrance 24 hours a day.
Video showing alleged shooter in Vienna attack
Oskar Deutsch, the head of the Jewish community in Vienna, said the synagogue was already closed at the time of the shooting.
Deutsch added the shooting took place in the street where the city's main synagogue is located but that it wasn't clear whether the house of worship had been targeted.
Nevertheless, Jewish community organizers appered to have sent phone messages to community members asking them to take off their kippahs in order to avoid being targeted.
Earlier, a police spokesman said a large police deployment is underway in central Vienna.
Kronen Zeitung said shots were ired in the area of a nearby square, Schwedenplatz.
First published: 22:03, 11.02.20