As a cross-harbour route that goes through the heart of Kowloon and densely populated Sham Shui Po and Kwai Chung, the line is very heavily travelled.

The original plan envisioned a terminus in a valley further west of the present Tsuen Wan station.

The line was supposed to run underground in Tsuen Wan rather than on the ground level, as is currently the case.

[5] The extension was formally opened on 10 May 1982 by Sir Philip Haddon-Cave, the acting governor and former chairman of the Mass Transit Railway Provisional Authority.

Upon the opening of the Island line, Chater, Waterloo, and Argyle, originally named based on the streets crossing or above the stations, Chater Road, Argyle Street, and Waterloo Road respectively, were renamed to Central, Yau Ma Tei, and Mong Kok, resembling the names of the station in Chinese.

When the Tung Chung line was constructed, Lai King was selected as an interchange so that passengers did not have to go all the way to Hong Kong Island to change trains.

To cope with extensions and new lines, Mei Foo and Tsim Sha Tsui stations had new subsurface walkways added to connect to KCR West Rail's Mei Foo and East Tsim Sha Tsui stations.

It is mostly underground, beginning at Central and crossing Victoria Harbour after Admiralty to Tsim Sha Tsui.

After Kwai Hing, the line re-enters the tunnel to Tai Wo Hau before ending at Tsuen Wan.

The same vendor also provided a similar signalling system in Singapore, which resulted in the Joo Koon rail accident in 2017.