At least one person has been killed and several injured in Vienna in what security officials described as a "terror attack".
"One deceased person, several injured (1 officer included)," police said on Twitter. "1 suspect shot and killed by police officers."
The Austria Press Agency earlier quoted ambulance service spokesman Daniel Melcher saying there were several dead and injured in the Austrian capital, though he was unable to provide a number.
Austria's top security official said authorities believe there were several attackers involved and the incident was ongoing.
"It appears to have been a terror attack," interior minister Karl Nehammer told public broadcaster ORF, adding that the perpetrators were armed with rifles.
"I can confirm that there were several injured and that there are probably also deaths among them," Mr Nehammer said.
Vienna police said several shots were fired shortly after 8pm local time in a lively street in the city centre, and that there were six different shooting locations.
Police urged people to avoid all open spaces and public transport in the city. Police said trams and buses were not stopping and urged social media users not to post videos of the 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."
Oskar Deutsch, the head of the Jewish community in Vienna, said the shooting took place in the street where the city's main synagogue is located but that it was not clear whether it had been targeted.
The synagogue was closed at the time of the shooting around, he said.
Rabbi Schlomo Hofmeister told the Associated Press he saw at least one person fire shots at people sitting outside bars in the street below his window.
"They were shooting at least 100 rounds just outside our building," Mr Hofmeister said.
"All these bars have tables outside. This evening is the last evening before the lockdown," he added.
"As of midnight, all bars and restaurants will be closed in Austria for the next month and a lot of people probably wanted to use that evening to be able to go out."