Dunedin Airport is about to begin a $13.5 million project to extend its departure lounge and security screening area after a surge in passenger numbers.

Work will begin next month on the project that will fill an empty space in the centre of the terminal, an area passengers do not usually see. Signal Management Group is leading the project as Dunedin Airport's project and construction manager. Project manager and Signal director Shokit Ali has been working on the project since mid 2017. Construction will be completed by the end of 2019.

The project is needed after the increasing numbers meant there was an "unacceptable" lack of room in the departure lounge and long queues through the terminal. The airport now deals with 1,035,645 passengers a year - a 47% increase since the terminal was built in 2006 - and during its busiest hour hosts more than 500. It takes 1734 more jets a year than it did in 2006, a 46% increase.

Airport chief executive Richard Roberts said the extension would be on the first floor only. It would triple the floor area of the departure lounge and more than double the security screening area. He said the project was expected to be finished by the end of next year. It would be "quite complicated" in terms of effects on passengers, but the airport would keep the public informed.

Mr Roberts said the airport had experienced "significant growth", particularly over the last three years, meaning the building had been under significant pressure.

A process of design was begun, as well as consultation with airlines, something required under the Airport Authorities Act. Those processes were completed, and "we have a project on our hands". Mr Roberts said the project had been designed to keep up with growth until about 2026."