British Transport Police are searching for a member of the public who jumped onto the tracks at Bank station yesterday to save a man's life.
BTP said they were looking for the "hero", who had risked his own life to save a "vulnerable" man, so they can thank him.
Officers were called to the southbound Northern Line platform at Bank station following reports of a man on the tracks just after midday yesterday.
"From speaking with witnesses at the scene, it appears a member of the public jumped onto the tracks and pulled the vulnerable man off the tracks as a train was approaching," BTP said in a statement.
"This brave and fearless act ultimately saved him from serious injury. The man then walked away."
Inspector Stacey Piper-Harfield from British Transport Police, said: "This was an incredibly selfless act of bravery, without a moment’s hesitation this man leaped to the rescue. He then walked away before officers could say thank you. Do you know the unknown Good Samaritan? Please get in touch.
"Whilst his actions undoubtedly saved this man’s life, jumping onto the tracks is extremely dangerous."
Anyone who can help the BTP to trace the hero is asked to get in touch via text on 61016 quoting reference 220 of 19/1.
Bank junction has been the site of a number of taxi driver demonstrations this week, as cabbies protest the City of London Corporation's plans to restrict their access to the area.