4 people stabbed in Vienna

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.

Police are still searching for the attacker or attackers, the spokesman said.

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.