A man has been taken to hospital after being Tasered by police during an alleged knifepoint robbery.
Nottinghamshire Police was called to Talbot Street, Nottingham, at 01:50 GMT where a man had a mobile phone taken during the incident.
Officers arrested two men, one in Waverley Street where the Taser was used, and the road was then shut.
The force has referred itself to the Independent Office for Police Conduct because the man was injured.
An officer was also hurt during the arrest and has been treated for a hand injury, while the suspect is being treated at Queen's Medical Centre.
Waverley Street, which is a tram route, was closed between the junctions with Peel Street and Cromwell Street after the arrest. This stopped trams running from The Forest to Clifton South or Toton Lane in both directions.
Steve Cooper, assistant chief constable from Nottinghamshire Police, said: "At just before 2am reports were received by police of a knifepoint robbery. Officers attended the scene where they arrested two men. One of which a Taser was deployed.
"That man was taken to QMC after being injured and as a result we have closed the street down and referred it, due to serious injury taking place, to the IOPC.
"He is at QMC on a normal ward where he is being looked after by medical professionals.
"A police officer was injured during the arrest and they received injuries to their hand."