Gunmen attacked six locations in central Vienna on Monday starting outside the main synagogue, killing two people and injuring at least 14 in what Austria called a "repulsive terror attack" while hunting one or more assailants on the loose.
Witnesses described the men firing into crowds in bars with automatic rifles, as many people took advantage of the last evening before a nationwide curfew was introduced because of Covid-19. Police shot and killed one assailant.
Police sealed off much of the historic centre of Vienna, urging the public to shelter in place. Many sought refuge in bars and hotels, while public transport throughout the old town was shut down and police scoured the city.
"It is the hardest day for Austria in many years. We are dealing with a terror attack the severity of which, thank God, we have not experienced in Austria in many years," Interior Minister Karl Nehammer told a news conference.
Austria's capital had so far been spared the kind of deadly militant attacks that have struck Paris, London, Berlin and Brussels, among others, in recent years. Chancellor Sebastian Kurz said the "repulsive" act was "definitely a terror attack", but he could not say what the motive was.
Oskar Deutsch, the head of Vienna's Jewish community, which has offices adjoining the synagogue on a narrow cobbled street dotted with bars, said on Twitter here that it was not clear whether the temple or offices were targeted but that they were closed at the time.
Rabbi Schlomo Hofmeister told London's LBC radio he was living in the compound of the synagogue. "Upon hearing shots, we looked down (from) the windows and saw the gunmen shooting at the guests of the various bars and pubs," he said.
"The gunmen were running around and shooting at least 100 rounds or even more in front of our building," he said.
Border checks were being reinforced, the Interior Ministry said, and children would not be required to attend school on Tuesday. Although people were urged to stay indoors Vienna Mayor Michael Ludwig told broadcaster ORF the city would run normally on Tuesday, albeit with a tougher police presence.
"According to what we currently know, at least one perpetrator is still on the run," Nehammer said.
"We have brought several special forces units together that are now searching for the presumed terrorists. I am therefore not limiting it to an area of Vienna, because these are mobile perpetrators," Nehammer earlier told ORF.
Kurz said the army would protect sites in the capital so the police could focus on anti-terror operations. Speaking to ORF, he said the attackers "were very well equipped with automatic weapons" and had "prepared professionally".
Videos circulated on social media of a gunman running down a cobblestone street shooting and shouting. One showed a man gunning down a person outside what appeared to be a bar on the street housing the synagogue. Reuters could not immediately verify the videos.
Condolences poured in from around the world, with top officials from the European Union, France, Norway, Greece and the United States expressing their shock at the attacks.
President Emmanuel Macron of France, which has seen two deadly knife attacks in Paris and Nice in recent weeks, issued a statement expressing shock and sorrow.
"This is our Europe," he said. "Our enemies must know with whom they are dealing. We will not retreat."
French officials have ramped up security since the attacks in Paris and Nice, which had suspected Islamist motives. Macron has deployed thousands of soldiers to protect sites such as places of worship and schools, and ministers have warned that other Islamist militant attacks could take place.
Robert O'Brien, President Donald Trump's national security adviser, said Americans were praying for the people of Vienna.
"There is no justification for hatred and violence like this. We stand with Austria, France, and all of Europe in the fight against terrorism," O'Brien said.
Democratic presidential candidate Joe Biden condemned what he called a "horrific terrorist attack," adding, "We must all stand united against hate and violence."
In 1981, two people were killed and 18 injured during an attack by two Palestinians at the same Vienna synagogue. In 1985, a Palestinian extremist group killed three civilians in an attack at the airport.
Nehammer is due to hold a news conference on the situation at 6 a.m. (0500 GMT) on Tuesday.