Three police officers had an unknown liquid thrown in their eyes as they responded to a fight in Leicester city centre.
Police believed that the substance may still be on the clothes of people in the area of King Street when the liquid was thrown, at around 4.50am on Sunday.
A 25-year-old man has been arrested on suspicion of administering a noxious substance and remains in police custody.
Police would like to hear from people affected and those who may have witnessed what happened.
DI Jenny Tattersall said: ‘The officers were taken to hospital after the liquid significantly irritated their skin and eyes. They have been monitored over several hours and discharged this morning.
‘While we don’t know what the substance is at this stage and tests will be carried out, medical professionals