Four people have been seriously wounded in two knife attacks in a district of Vienna but a motive or any connection between the assaults is unclear, Austrian police say.
The stabbings occurred on Wednesday night in Vienna's Second District, which includes the famous Prater park as well as the Praterstern transport hub.
It also houses much of Vienna's small Jewish community.
"A man attacked a family - a father, a mother and their 17-year-old daughter - with a knife. The three people were seriously injured and their lives are in danger," the spokesman said, adding later they were Austrian citizens.
"And half an hour later, there was another attack ... at Praterstern and here a person was also seriously injured and their life is in danger. We do not know to what extent there is a connection here and any motive remains unclear," he said.
Asked what was known about an assailant, he added: "Absolutely nothing. We know we are looking for a man."
A male citizen of Afghanistan was later arrested in connection with the second assault but no further details were immediately available and any connection between the stabbings remained unclear, a police spokesman said.
Vienna has not experienced deadly attacks by Islamist militants like the ones that have struck Paris, Berlin and Brussels since 2015.
Australian Associated Press