It will more than double the floor area of the terminal to 3800sq m, making room for a larger lounge, new check-in area and facilities, and a bigger cafe.
The $12.7m cost was being funded from the airport's cash reserves and future commercial revenue.
To date, half of the lounge floor slab has been laid and glue-laminated beams for the area were delivered this week, Dumble said.
The next major stage of the project will get under way this week.
The old gates will be demolished, allowing for the completion of the departure lounge floor slab and the erection of the beams.
This work meant temporary changes for the route passengers take between the terminal and their plane.
From Friday this week, passengers will temporarily use a tunnel to the tarmac a little further down the terminal than the existing gates, which will be demolished.
Dumble said the terminal area near the old gates would be extended by 25m, leaving passengers with a much shorter walk across the tarmac than they had now.
An artist's impression of the exterior of the upgraded terminal building at Tauranga Airport. Image supplied / TCC
There had been no disruptions to terminal operations during construction, he said, apart from temporary pathways and windows having to be blocked off for safety during construction.
Reaction to the expansion from frequent fliers and tourism leaders was positive last year.
Fliers looked forward to bigger, better facilities, while a tourism marketer said the upgraded terminal would give travellers a better first impression of Tauranga.
The expansion will accommodate an increase in Air New Zealand passenger volumes and provide for other regional network operators to fly in and out of Tauranga.
Earlier this month Air New Zealand announced it was adding more early morning flights between Tauranga and two main centres for business travellers: Auckland and Wellington.
New Wellington flights were scheduled to begin in April. The finalised new flights schedule, which would be revealed progressively, would see a total of 87 return flights between Tauranga to the two cities each week.
