PSNI Chief Constable Matt Baggott said that some of the violence was intense and there was t.
It was fortunate someone was not seriously injured, he claimed, adding that the situation in some areas was very tense.
There has to be a collective voice to bring this to an end.
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The man, in his thirties, was found with stab injuries on the upper deck of a bus in Handsworth, Birmingham, on Monday night.
Thousands of passengers now face delays, with Southeastern trains warning "all services" would be affected.
Paramedics attended a scene in Willesden, north-west London, on Monday afternoon where they found the teenager with stab wounds.