Ensuring Auckland copes with growth and has enough offices, apartments and shops is one of the biggest challenges the city faces, according to Auckland Council's chief economist Geoff Cooper.

The city centre commanded a significant productivity premium over the rest of New Zealand and so ensuring the growth of this area was an important issue for the entire country, Cooper said.

He was commenting after Colliers International released a study showing Auckland needed the equivalent of 54 buildings of the scale of the PwC Tower, Metropolis block and the Downtown mall in a little under two decades to cope with another 500,000 people.

"Ensuring adequate access into the city centre is a significant infrastructure challenge to growth forecasts.

"Over the next few years this means investing in the electrification of the rail network, a redesigned and more efficient bus network and the city rail link - but more will be needed in the decades to come," Cooper said.

Colliers found that by 2031, the CBD population was expected to make up 2.4 per cent of Auckland's total population, compared with 1.6 per cent in 2011, Cooper noted.

"This is the beginning of an important shift in Auckland. We are beginning to see a new phase of apartment building coming through and as the city centre matures we can expect this to continue in the years to come," he said.

"It is not just about hard infrastructure, though. The city centre also needs world-class urban spaces and parks as well as adequate space for retail to activate economic activity and attract new businesses and employees," he said referring to Auckland's City Centre Masterplan.

Cooper said: "All this requires developers to bring on new commercial and apartment buildings when the demand exists.

"The increase in supply of such commercial and apartment stock is required to ensure prices remain affordable for those wanting to live and work in the urban centre."