Police in riot gear were called to an estate in Wrexham last night after a large crowd gathered.
Officers said missiles were thrown at them and cars and property were damaged.
North Wales Police confirmed it was dealing with an ongoing incident at 11.40pm last night and a police helicopter was seen flying above the Caia Park estate.
Police said it happened because a number of people gathered in Wynnstay Avenue "to protest against an individual they wrongly thought to be present there".
A local resident said: "It started as a peaceful protest that got out of hand when large groups started arriving."
Superintendent Owain Llewellyn said: “Our priority was ensuring the safety of people in the area and there was at one point a large number of officers there whilst we worked to calm the situation which had escalated quickly.
"Missiles were thrown at officers, although thankfully none were injured, but damage was caused to cars and property."
Superintendent Nick Evans added: “Sadly last night we were called to deal with a situation where a number of people gathered in Wynnstay Avenue to protest against an individual they wrongly thought to be present there.
“Whilst everyone has a right to peaceful protest, this incident resulted in wholly unacceptable behaviour which included items being thrown at officers. Whilst thankfully none were hurt, cars and property were damaged.
“The actions of those involved have understandably caused a lot of distress locally and we will be working in partnership with our council colleagues to reassure the wider Caia Park community that their safety is our priority and we will do all we can to prevent this happening again.”
Ian Bancroft, Chief Executive with Wrexham Council, said: “We would like to reassure the community that we will be working with North Wales Police in response to this incident as they continue their investigations. It is not appropriate for us to comment on any individuals involved.”
An investigation into the offences committed last night has begun and police are appealing to anyone with information to contact them via the website or by calling 101.