A final decision has not been made, but The Straits Times understands that the plan is for both the future Thomson-East Coast Line and Cross Island Line to be linked to the new mega passenger terminal.

When this happens, it is likely that the existing MRT link between Singapore Expo and Changi Airport will cease to operate.

Currently, commuters going to the airport have to alight at Tanah Merah station on the East-West Line and take a shuttle train from a central platform to the airport.

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The Thomson-East Coast Line - scheduled to open in stages from 2019 to 2024 - is likely to stop at the future T5 before terminating at the existing Changi Airport MRT station. As for the Cross Island Line, targeted to be completed by 2030, the plan is to link the line to Changi East's new industrial zone before it heads to T5.

The possibility of extending the new lines to Changi Airport was first revealed by Transport Minister Khaw Boon Wan in July at an MRT groundbreaking ceremony.

He said then that an extension of the Cross Island Line to the airport would also complement the future high-speed rail link between Kuala Lumpur and Singapore, as the MRT line will be linked to the high-speed rail's Jurong East terminus.

T5, slated to open before the end of the next decade, is being built in Changi East, which is now separated from the existing airport terminals by Changi Coast Road. The new terminal will eventually be bigger than T1, T2 and T3 combined.

The Changi East development will include a new industrial zone that will house aerospace and other aviation-related businesses.

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A direct train link between the city and Changi Airport is a must, transport experts said.

Many other Asian airports, including those in Bangkok, Tokyo, Shanghai and Hong Kong, provide a rail option - in some cases, an express service - for travellers and visitors.

National University of Singapore transport researcher Lee Der Horng said that, while some may argue that an express service is less critical in Singapore, given the proximity of the airport to the city, travellers and visitors still expect good train and other transport links to and from Changi.

"It would be a wise move to extend the Thomson-East Coast and Cross Island lines to Changi East," he said.

Building a station at Changi East's future industrial zone would be a boon for airport workers too, said Singapore Aircargo Agents Association chairman Steven Lee.

"The existing air freight terminal that is near the airport is very inaccessible by public transport, which makes it inconvenient for the thousands of workers based there.

"If there is an MRT station at the new industrial zone, it would be great news for the workers," he said.