The developer of a planned office tower will add extra floors to what will be central Christchurch’s biggest new office building this century.

Countrywide Properties received approval last year to build 12 storeys high on its Worcester Bld site, but had now been granted resource consent to build 14 storeys and widen some of the floors. The site is next to the Christchurch City Council headquarters and opposite the city’s art gallery.

Director Richard Diver said the finished building could be worth about $200 million.

It is one of several office building projects under way in the central city, as strong economic growth boosts demand for premises.

Vacancy rates in central Christchurch office buildings have fallen to 7.4%, compared with rates of 18.4% for Auckland and 17.7% for Wellington, according to real estate firm CBRE. This has led to Christchurch’s office rents rising while those in Auckland and Wellington have fallen.