BERLIN (Reuters) - A German man was dragged beneath a tram for more than 3km and through seven stations, as passengers heard his screams but did not initially realise where the noise was coming from, the police said on Tuesday.

The 20-year-old lost both legs and an arm in the 10-minute ordeal that left a trail of blood through the city of Dortmund. It ended when a passenger finally pulled the streetcar's emergency brake, Bild newspaper reported.

The man was unconscious when he was extricated and taken to hospital in critical condition.

"Several passengers later said they had heard his cries for help but couldn't tell where they were coming from," Dortmund police said in a statement.

Jan Norman, 20, was trapped upside down between the couplings when he attempted to leap between two tram cars, The Daily Mail reported.

A medic at the scene said: "The poor guy had literally been flayed alive during this nightmare."

Blood pooled at each of the six stations the tram stopped at, but no one alighting or getting on the tram, nor any passers-by saw him.

A friend who was with him screamed after the tram: 'My friend is dying! For God's sake stop!'

At the sixth stop, a newspaper kiosk owner finally saw Mr Norman and banged on the side of the tram.

The tram was moving to the seventh station when the passengers on board pulled the emergency stop lever.

He was no longer conscious when police and paramedics arrived to free him.