A man in his 60s suffered serious head injuries when he was assaulted in Croydon town centre this afternoon.
A second man was arrested on suspicion of causing grievous bodily harm after the assault in Tamworth Road at just before 2.10pm.
Paramedics took the injured man to St George's Hospital in Tooting as a priority.
Trams have been suspended between Reeves Corner and East Croydon while police investigate the attack, which took place on the tracks.
A Metropolitan Police spokesman said: "We can confirm that police were called at 2.10pm on Monday, 17 February to reports of an assault in Tamworth Road, Croydon.
"A man in his sixties was assisted at the scene by LAS after he sustained head injuries; he has been taken to a South London hospital.
"Officers have arrested a man at the scene on suspicion of GBH."
TfL said services it expected trams to resume by 6.15pm.
Do you know more about this story? Email firstname.lastname@example.org or call 020 8722 6351.
- Bomb scare as “suspicious item” seen near Croydon supermarket
- This American football star was trafficked into the UK and left homeless - now he has gone from Croydon to the NFL
- Mum quit her job to take son to school in Vauxhall because of a Croydon Primary's 'unacceptable' admissions policy
- Crystal Palace Beer Festival is returning with 150 beers and 50 ciders to get stuck into
- Armed forces deployed in London in response to critical terror alert