Airports of Thailand Plc wants the AoT board to agree to demolishing the old, disused terminal at Don Mueang and replacing it with a new, larger facility to cope with the ever-growing number of international passengers.

The new Terminal 3 building would serve international passengers, whose numbers spiked 14% last year compared with the 1% increase in domestic travellers using Don Mueang, an AoT source said before the board meeting on Wednesday.

Terminal 1 was renovated earlier to handle international flights and Terminal 2 for domestic travel, but the first is still "too narrow" to handle the number of tourists, mostly tour groups from China, the source told Thai Post Newspaper.

The AoT board earlier resolved to renovate the old terminal, which has been unused since 2006, and use it to handle domestic traffic, under the five-year Don Mueang Airport upgrade plan, with work scheduled to start in 2020.

However, the rapid increase in international passengers has led to overcrowding and caused the AoT to reconsider the plan, believing priority should be given to international travellers.

The agency decided it was better to knock down the old building, because just "dusting it off and repainting it are not enough", the source said. That would only bring the same overcrowding problem now occurring at Terminal 1.

If the AoT board greenlights the demolition plan, AoT plans two years for construction of the new building and opening it in 2021.

The new terminal is expected to be able to handle 40 million passengers a year.

During its construction, the AoT plans to ask the board to approve building a temporary extension near Terminal 1 to handle the overflow of international passengers, the source added.