Parallel trading in Hong Kong refers to the phenomenon of China parallel traders taking advantage of multiple entry visa policy to import goods from Hong Kong to Mainland China, causing shortage of household goods in various locations starting in the North District and expanding to Tuen Mun, Yuen Long, Tai Po and Shatin. Problems relating to this include increased congestion from the millions of day traders, overloading of infrastructure and disruption of the everyday lives of residents in northern districts of Hong Kong. Demand of significant volumes of daily necessities favoured by Shenzhen residents have progressively squeezing out those catering to local needs, and caused rent inflation and shortage of certain goods such as infant formula.