Construction of the Modified Initial System (now part of Kwun Tong Line and Tsuen Wan Line) commenced in November 1975. After almost four years, the northern section was completed on 30 September 1979. On 1 October 1979, the northern section was opened, with trains running from Shek Kip Mei to Kwun Tong. The route from Tsim Sha Tsui to Shek Kip Mei was opened in December of the same year.