Which country are you referring to? In the UK immigrants mainly settled in industrial cities as they were unskilled workers and there were a lot of labouring jobs available. The immigrants are preferable for these jobs as they are willing to be paid less. Ethnic neighbourhoods can sometimes have high crime rate as they have clashes in culture with different ethnicities and also with the locals whilst also often being poorer areas which also tends to cause an increase in crime rate. This is only the tip of the iceberg but hopefully it helps in finding the full answer to your question and it's applicable to your location of interest.
