The contract for the high-speed railway set to link Don Mueang, Suvarnabhumi and U-tapao airports will officially be announced and signed by the winning bidder by next January, the State Railway of Thailand (SRT) has announced.

The railway operator's acting governor Voravuth Mala made the comments Monday during a second pre-tender meeting, comprising representatives from all 31 previously announced firms that purchased bidding documents.

The documents, which were up for grabs in June and July, cost each firm one million baht to obtain.

The SRT's timeline for the 224-billion-baht, high-speed airport link states that tender documents should be submitted by the firms on Nov 12.

"By that evening [Nov 12], we will have the official list of bidders for the project," Mr Voravuth said, adding that the authority will also find out which firms have decided to group together to make bids.

Current plans and contract bidding papers call for a 220-kilometre, 250kph railway linking the three main Bangkok-area airports.

"So far, we have received over 600 questions from the firms, half of which we have already answered," Mr Voravuth said. "Most of the questions involved some confusion regarding the tender instructions, land acquisition and commercial developments around the route."

Upon its completion, the airport-linking railway will be approximately 220km-long, with its trains reaching up to 250kph, according to initial SRT reports.

It is set to link Don Mueang airport to U-tapao airport in Rayong, through a route that will also see it stop at Suvarnabhumi in Samut Prakan, completing the three-airport connection.

The network will use the current Phaya Thai-Suvarnabhumi Airport Rail Link's (ARL) and extensions will be built to Don Mueang and U-tapao.

The mega-project was fast-tracked as part of the government's plans to develop the Eastern Economic Corridor (EEC), which comprises Chachoengsao, Chon Buri and Rayong.

However, Mr Voravuth said the project must first pass an environmental impact assessment (EIA) from the Office of Natural Resources and Environmental Policy and Planning before any contract-winner can ink an agreement with the SRT.

The acting chief said the railway network must take no more than five years to complete after the contracts are signed, adding he expects the network to be open by the end of 2023.