Police on patrol came across a group of teens fighting on a U4 bus on Station Road in the town centre.
Two teenagers suffered head injuries with one 14-year-old boy being taken to hospital.
The second teenager was discharged by paramedics at the scene.
A 15-year-old was arrested on suspicion of causing grievous bodily harm and has been bailed while police enquiries continue.
A London Ambulance Service spokesperson said: “We were called at 2.22pm on Tuesday 10 June to reports of an assault on Station Road, Hayes.
“We sent ambulance crews to the scene.
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“We treated two teenagers for head injuries. We took one patient to hospital and discharged the other at the scene.”
A Met Police spokesperson said: “At 15:32hrs on Tuesday, 10 June police on patrol came across a fight between a number of teenagers on board a bus in Hayes Town Centre, Station Road.
“A 14-year old boy required outpatient treatment for minor injuries.
“A 15-year-old boy was arrested at the scene on suspicion of causing grievous bodily harm. He has been bailed while enquiries into the circumstances continue.
“Anyone with information that could assist police is asked to call 101 or ‘X’ @MetCC and quote CAD4711/10Jun.
“You can also provide information anonymously via the independent charity Crimestoppers on 0800 555 111.”
