A large area of central Vienna was cordoned off. Police said a significant deployment was under way and that they had shot dead the suspect. They urged people to stay inside.
Interior Minister Karl Nehammer told Austrian broadcaster ORF that it was “an apparent terror attack”.
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 after 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.
Jewish community leader Oskar Deutsch said on Twitter that it was not clear whether the Vienna synagogue and adjoining offices had been the target of the Vienna attack, and said they were closed at the time.
Videos circulated on social media of a gunman running down a cobblestone street shooting and shouting. Reuters could not immediately verify the videos.
In 1981, two people were killed and 18 injured during an attack by two Palestinians at the same synagogue. In 1985, a Palestinian extremist group attacked Vienna airport with hand grenades and attack rifles, killing three civilians.
In recent years, Austria has been spared the sort of large-scale attacks seen in Paris, Berlin and London.
In August, authorities arrested a 31-year-old Syrian refugee suspected of trying to attack a Jewish community leader in the country’s second city Graz. The leader was unhurt.
