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.
- Firefighters called to 2am bin fires twice in two weeks
- Woman robbed by men who offered her lift in car
- Take a journey through history of the BBC in theatre show
- London Victoria services delayed due to earlier broken down train
- Pensioner racially abused betting shop worker and hit her with walking stick after she refused to let him use the toilet