Police have arrested a 14-year-old girl after an 87-year-old woman was allegedly punched in the face on a London bus.

CCTV footage was released earlier on Monday which appeared to show the elderly woman talking to two teenagers, who police said had boarded the bus without paying.

The elderly woman can be seen getting up out of her seat, after which one of the two girls appears to hit her in the face. Both girls then left the bus.

The victim received a black eye in what police called the "nasty attack on an elderly woman who just wanted to get home" and was taken by ambulance for treatment at St Helier Hospital after another passenger came to her aid.

In a statement, a Metropolitian Police spokesperson said a female suspect had been arrested on suspicion of causing actual bodily harm (ABH).

"The 14 year-old female has been taken to a south London police station where she remains in custody," the spokesperson said.