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.
- House of Reeves owners have home ransacked and precious jewels stolen
- Lorry driver caught bringing undeclared alcohol into UK from France has licence suspended
- Winners of our Young Reporter scheme for 2015 celebrated at awards
- Large office block to make way for mixed development including more than 30 affordable homes
- Homeowners in SW19 and nearby can net thousands of pounds from Wimbledon tennis tournament