Lee says Wellington's secondary vacancy rate has also dipped by 3.3 per cent, with only 103,147sq m (9.1 per cent) of secondary stock available now compared with a year ago.
Lee questions whether new office supply in Wellington this year will be able to alleviate some of the demand pressures.
"The completion of new office developments in Wellington last year totalled 38,800sq m. One of the largest additions was the new Transpower building at 22 Boulcott St (8440sq m), which allowed the tenant to consolidate two office locations.
"However, the new stock has done very little to alleviate demand, and vacancy is unlikely to lift any time soon.
"While both 20 Customhouse Quay and the new PwC Centre are expected to be completed by mid-year, almost all of their 26,400sq m of new office space has been pre-committed."
Lee says Wellington's low office vacancy rates have seen average prime gross face rents increase 3.9 per cent in the year to December 2017.
"It's certainly a great time to be a landlord in the prime office market in Wellington," he says. "That sentiment is reflected in Colliers' latest quarterly investor confidence survey, which found Wellington was the only main centre to record an improvement in office investor confidence."
In Auckland's CBD, office vacancy increased 0.7 per cent to 5.9 per cent overall in December 2017, but continues to remain low. It has not exceeded 6 per cent since the middle of 2015.
The latest increase stems mostly from more prime stock becoming available in Viaduct Harbour and Victoria Quarter.
The next two years will see close to 60,000sq m completed over three projects, but vacancy will remain tight over this period.
Vocus House on Sale St is set to be completed this quarter, while the majority of new office supply is set to arrive in Q3 2019. PwC Tower in Commercial Bay makes up over half (39,000sq m), while One 55 Fanshawe, to be constructed on the ex-Caltex site by Mansons TCLM, is expected to contribute 15,000sq m.