The Kwun Tong Line was extended across the harbor to Quarry Bay , which became an interchange station for the Kwun Tong Line and the Island Line . The extension was launched on 5 August 1989 . The Kwun Tong Line was extended across the harbor on 5 August 1989 to Quarry Bay Station , which became an interchange station for the Kwun Tong Line and the Island Line .