An officer blocks a street when police is on the hunt for an attacker after several people have been injured in a knife attack on the streets of Vienna, Austria, Wednesday, March 7, 2018. (AP Photo/Ronald Zak)
(CNN) -- Police said four people were injured Wednesday in two separate knife attacks about 30 minutes apart in central Vienna, Austria.
Three victims were injured in the first attack outside a restaurant near the Nestroyplatz subway station, a police spokesman told CNN. The victims were a couple and their daughter, CNN affiliate ORF reported.
The fourth victim was injured in the second attack at Praterstern, a major city square, the spokesman said. Authorities are investigating whether the incidents are linked, the spokesman said.
An "Afghan male" was arrested in connection with the attack in Praterstern, Vienna police spokesman Patrick Maierhofer told CNN. The suspect stabbed a Chechen national, causing life-threatening injuries, Maierhofer said.
It was not clear if the suspect was connected to the first stabbing, Maierhofer added. He said police continue to investigate the stabbings with the help of surveillance videos and eyewitnesses.
Witnesses said they saw police swarming the area. Michael Eisenriegler, who lives next to where the stabbing happened, told CNN he saw flashing lights and went downstairs.
"There were maybe ... one or two dozen policemen (at the site of the attack.) And they are still there," he said.
"(The road) is blocked. They are searching," Eisenriegler said.
Clemens Oistric, a journalist at Austrian newspaper Heute, said he was in his office nearby during the attack.
"People shouted because three people were hit by a man who had a knife. They're in hospital," Oistric said told CNN.
CNN's Elwyn Lopez and Anna Maja Rappard contributed to this report.