Auckland Airport has unveiled a $3.9 billion redevelopment project, which will see it combine its domestic and international terminals.

The airport said the project would replace the 57-year-old domestic terminal, at a cost of $2.2b and it was set to open between 2028 and 2029.

The rest of the cost ($1.7b) is for other projects associated with the integration and includes forecast increases in construction costs and holding costs.

The airport planned 12 new domestic aircraft gates, up 20 percent from current levels, with electric charging and all catered for future aircraft.

It said the combined terminal would see a five-minute transfer between the domestic and international areas.

It would also have additional retail and rest areas, a new "state-of-the-art" check-in area, and a smart baggage system, using 50 percent less power to process each bag compared to a conventional conveyor-based system.

A graphic showing how the Auckland Airport redevelopment will result in the domestic and international terminals coming under one roof.

Auckland Airport chair Patrick Strange said it was a major investment for the airport, many years in the making.

"The domestic terminal is almost 60 years old and needs replacing. It's nearing capacity and it's no longer fit for purpose and hasn't been for some time. If it wasn't for the pandemic, we would already be well underway with its replacement," Strange said.

The airport has consulted with its major airline customers on a replacement terminal since 2011.

"We have worked with major airlines for over a decade on this. We've considered all feedback, including potential alternative locations and even further delays to infrastructure development," Strange said.

"All of this has been carefully thought through and we have made changes where appropriate, but now we need to get on with it," he said.

Construction would take place over the next five to six years.

Auckland Airport chief executive Carrie Hurihanganui said the project was about building the gateway Auckland and New Zealand needed.

"A new domestic terminal integrated into the international terminal will make Auckland Airport fit for the future, providing a much-improved experience for travellers - something they've clearly and repeatedly told us they want," she said.

Renovations would "not cut it anymore", she said.

The redevelopment would employ 2000 additional customers at the height of construction.

The airport is currently consulting with airlines on new aeronautical charges between July 2022 and June 2027.

It said the terminal integration programme was a major part of its 10-year capital programme, which informed overall airport pricing.