Rotorua's Mayor says it's incredibly disappointing two teenage girls were separately assaulted outside the local library

A 15-year-old was set upon by three others on Monday, and a 13-year-old punched by a stranger last Thursday, while waiting for a bus.

Mayor Tania Tapsell says the latest attack may be gang-related - with a suggestion the colours worn by the victim were a factor.

She says unfortunately, this is the result of young people making very poor decisions - with an increase in offending, both assaults and ram-raids.