Four people are critically injured and fighting for their lives in hospital after two knife attacks in the Austrian capital, Vienna.A police statement said a man, 67, woman, 56, and their teenage daughter, 17, were stabbed on Praterstrasse by the Nestroyplatz metro station in the heart of Vienna at around 19:45. The attacker then fled towards Praterstern police said. In a second incident at around 20:15, a 20-year-old man was stabbed at nearby Praterstern transport hub.