The Quarry Bay Congestion Relief Works extended the Hong Kong Island end of the Kwun Tong Line from Quarry Bay to North Point via a pair of 2.1-kilometre , total of 4.2 -- kilometre tunnel .
The Quarry Bay Congestion Relief Works involved extending the Hong Kong Island end of the Kwun Tong Line from Quarry Bay to North Point via a 4.2 -- kilometre tunnel .