The 26-year-old man suffered life-threatening head injuries and underwent emergency surgery in hospital, but remains in a critical condition.

Witnesses said the man snatched an elderly woman’s handbag at 5:30am, as she was going down the stairs to the platform.

The 62-year-old woman fought back and held onto her bag, but the handle ripped during the scuffle and the woman fell down the stairs.

The man ran onto the platform with her bag, jumped onto the train tracks and ran off in the direction of Karlsplatz. In the tunnel he was hit by a train travelling towards Hütteldorf, on the opposite track.

"The driver said that he heard a loud bang and assumed that he had driven over an iron bar. He immediately put the brakes on and did an emergency stop," police spokesman Paul Eidenberger said.

Police said the train did not run over the man, but hit him head on. He was unresponsive when a medical team arrived and was taken by helicopter to hospital.

According to a report in the Kronen Zeitung newspaper the man was an Algerian asylum seeker from the Traiskirchen refugee centre.

The woman’s handbag was found on the train tracks. She was examined in hospital after complaining of rib pain and breathing problems but suffered nothing more serious than bruising.

The U4 line was briefly suspended between Pilgramgasse and Landstrasse but normal service resumed at around 6:45am.