Several weeks later, in early 1975, a government agency known as the Mass Transport Provisional Authority was established to take charge of the project. It announced that the Initial System would be slightly reduced to 15.6 kilometres, and renamed it the Modified Initial System. Plans for a single contract were also abandoned in favour of 25 engineering contracts and 10 electrical and mechanical contracts.
In addition, the government-owned Hong Kong Mass Transit Railway Corporation (MTRC) was established to replace the Mass Transport Provisional Authority. (This was the company succeeded by the MTR Corporation Limited on 30 June 2000)
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.
In 1980, the first harbour crossing was made by an MTR train as the Kwun Tong Line was extended even farther to Chater station, now known as Central station. To deal with increasing patronage, trains were also extended to six cars.
The government approved construction of the Tsuen Wan Line in 1977, then known as Tsuen Wan Extension, and works commenced in November 1978. The project added a 10.5-kilometre section to the MTR system, from Prince Edward to Tsuen Wan. The line started service on 10 May 1982 with a total cost of construction (not adjusted for inflation) at HK$4.1 billion.
When service of this line started, the section of the Kwun Tong Line from Chater to Argyle, present-day Mong Kok station, was transferred to the Tsuen Wan Line. Thus, Waterloo became the terminus of the Kwun Tong Line, and both Argyle and Prince Edward stations became interchange stations. This change was made because system planners expected traffic of the Tsuen Wan Line would exceed that of the Kwun Tong Line. This forecast proved quite accurate, necessitating a bypass from the northwestern New Territories to Hong Kong Island. Launched in 1998, the Tung Chung Line serves exactly that purpose.
Although land acquisitions were made for a station at Tsuen Wan West, the station was never built. This is not to be confused with Tsuen Wan West Station on KCR West Rail, which lies on the newly reclaimed area near the former ferry pier.
It is interesting to note that since the line's opening in 1982, this is the only line whose alignment has virtually remained the same for the past 23 years. For example, the Kwun Tong Line's alignment has changed for 2 times since its opening - the taking over of Tsuen Wan Line from Mong Kok to Central, and the taking over of Eastern Harbour Crossing section by the Tseung Kwan O Line.
Government approvals were granted for construction of the Island Line in December, 1980. Construction commenced in October, 1981. On 31 May 1985 the Island Line was opened with service between Admiralty and Chai Wan stations. Both Admiralty and Central stations became interchange stations with the Tsuen Wan Line. Furthermore, each train was extended to eight cars.
On 23 May 1986, service reached Sheung Wan station. Construction for this station was delayed for one year as government offices which sat on top of the station had to be removed to a new location before construction could start.
In 1984, the government approved the construction of the Eastern Harbour Crossing, a tunnel to be used by cars and MTR trains. The Kwun Tong Line was extended across the harbour 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. An intermediate station, Lam Tin, started operations on 1 October 1989.
The decision was made in October 1989 to construct a new international airport at Chek Lap Kok on Lantau Island to replace the overcrowded Kai Tak International Airport. The government invited the MTR to build a train line, then known as the Lantau Airport Railway, to the airport. But construction did not begin until the Chinese and British governments settled their financial and land disagreements in November 1994.
In the end, the new line was included in the financing plans of the new Hong Kong International Airport as the airport was not considered viable without direct public transport links. Construction costs were also shared by the MTR which was granted many large-scale developments in the construction plans for the new stations.
The Lantau Airport Railway turned into two MTR lines, the Tung Chung Line and the Airport Express. The Tung Chung Line was officially opened on 21 June 1998 by Hong Kong Chief Executive Tung Chee Hwa, and service commenced the next day. The Airport Express opened for service on 6 July 1998 along with the new Hong Kong International Airport.
The Airport Express line is the second most popular means of transport to the Hong Kong International Airport. In 2005, 22% of the commuters took the Airport Express to and from the airport.
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. The project was initiated due to overcrowding at Quarry Bay and persistent passenger complaints about the five-minute walk from the Island Line platforms to the Kwun Tong Line platform. Construction began in September 1997 and was completed in September 2001 at a cost of HK$3.0 billion (US $385 million). The tried-and-true cross-platform interchange arrangement is repeated here.
Construction of the Tseung Kwan O Line was approved on 18 August 1998 to serve new housing developments. Construction began on 24 April 1999 and the line officially opened in 2002, taking over the train tracks running through the Eastern Harbour Tunnel from the Kwun Tong Line, running from Po Lam to North Point. When the line was opened, the Kwun Tong Line was diverted to Tiu Keng Leng on the new line. Construction costs were partly covered by the Hong Kong Government and private developers which linked construction of the Tseung Kwan O Line to new real estate and commercial developments. Previously less developed areas were opened up for development with more transport options.
While the construction of the Tung Chung Line was still underway, the plan to build a railway corridor serving the northwestern New Territories was conceived. Space had been reserved for the addition of an interchange station and two extra tracks (to allow nonstop service for the Airport Express) between Olympic and Lai King. Originally known as the Airport Railway Phase 2, the contracts of the West Rail Line Interface Works were awarded shortly after construction works of the West Rail commenced. The project comprised Mei Foo Interchange (modification of the existing Mei Foo station on the Tsuen Wan Line to provide a pedestrian link to the West Rail Line Mei Foo Station); Nam Cheong Station (an interchange station on the Tung Chung Line, jointly operated by the MTRCL and KCRC) and quadruplication works (the additional two tracks, four kilometres in length, allow the Tung Chung Line trains to stop at Nam Cheong without blocking the passage of Airport Express trains).
The works were completed in stages. The Tung Chung Line trains have been diverted to the new track since mid May 2003, whereas the Mei Foo station interchange subway and the Nam Cheong station were opened at the same time the West Rail Line opened for public use in December 2003. The Kowloon Southern Link extension from Nam Cheong Station to East Tsim Sha Tsui Station was opened on 16 August 2009, with West Rail Line trains now terminating at Hung Hom Station, interchange station for East Rail Line.