Opened on 1 October 1979 as the first urban railway line in Hong Kong and the first operated by the Mass Transit Railway Corporation (MTRC), the Kwun Tong line operates over much of the original section of the "Modified Initial System", from Shek Kip Mei to Kwun Tong station, which it is named after. The line has seen the most changes in alignment of all the MTR lines, the most recent in 2016. It has crossed Victoria Harbour to serve Hong Kong Island using two separate routes in its history, though other lines have since taken over the harbour crossings; as such, the current route lies entirely within Kowloon except for Tiu Keng Leng in the New Territories. It has interchanges with four other lines: the Tsuen Wan line, the East Rail line, the Tuen Ma line, and the Tseung Kwan O line.