Although not in regular service, the original tunnel linking the Kwun Tong line to the Eastern Harbour Crossing continues to be maintained and can be utilised in the event of a disruption on the Tseung Kwan O line. Such an incident occurred on 16 December 2013, when a train on the Tseung Kwan O line broke down, halting train services on the entire line for several hours. To prevent cross-harbour train service from being disrupted, all Kwun Tong line trains temporarily used the old tracks from Lam Tin to Quarry Bay and terminated at North Point, as they did before the opening of the Tseung Kwan O line. This was the first time since 2002 that the Lam Tin to Quarry Bay tracks were utilised for regular service.