A teenager has been arrested after a taxi driver had an unknown substance sprayed in his eyes, causing serious injuries.
The attack happened in High Wycombe when the driver caught up with three people who left his black Toyota Prius on George Street without paying at around 1am on Sunday.
A 15-year-old boy was later arrested on suspicion of causing grievous bodily harm with intent.
The victim, 43, is in hospital and police are still trying to identify what was sprayed in his eyes.
"This is an unprovoked attack on a working man who was going about his evening shift as a taxi driver," said Detective Chief Inspector Kelly Glister.
"It is cowardly for a group to attack an individual, especially when they use a weapon."
"The offenders are three black males aged between about 16 and 18 years old," added Inspector Glister.
"I understand that this attack will cause great concern in the local community but I want to reassure the public that the Thames Valley Police is conducting a thorough investigation and is determined to find the offenders."
Police are appealing for anyone with information about the attack to contact them on 101, or anonymously via Crimestoppers on 0800 555 111.