A big build's underway in Auckland to cope with more people being packed into the city.

Auckland Central's density has increased to 18,000 people per square kilometre, 1,000 times the New Zealand average.

Colliers International National Director Alan McMahon said more than 10,000 apartments are due to be completed in the city before 2020.

"In the CBD its quite easy because there's so much amenity here already. Public transport, retail, which makes high density apartment acceptable or the preference for many people," he said.

Figures released this week from Statistics New Zealand show that Auckland is the fastest growing city in the country, the population increasing by 2.6 per cent.

It also has the lowest median age in the country, with half the city's population under 34.

A big build's underway in Auckland to cope with more people being packed into the city.

Auckland central's density has increased to 18,000 people per square kilometre, 1,000 times the New Zealand average.

Colliers International National Director Alan McMahon said more than 10,000 apartments are due to be completed in the city before 2020.

"In the CBD its quite easy because there's so much amenity here already. Public transport, retail, which makes high density apartment acceptable or the preference for many people," he said.

Figures released this week from Statistics New Zealand show that Auckland is the fastest growing city in the country, the population increasing by 2.6 per cent.

It also has the lowest median age in the country, with half the city's population under 34.