A multi-storey office block will be blown up in quake-hit Christchurch's first controlled demolition next month.

The 14-storey Radio Network House building in Worcester St, which housed Newstalk ZB, will be razed with an explosive implosion.

The controlled demolition, which has been approved by the Canterbury Earthquake Recovery Authority (Cera), will be the first of its kind in the city since authorities began the massive task of bringing down the hundreds of quake-damaged buildings.

Most of the tall buildings have been brought down floor-by-floor, in a painstakingly slow process mainly because demolition contractors are working in confined city spaces that rule out implosions.

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Scheduled for Sunday, August 5, the potentially spectacular event is expected to attract a huge crowd of onlookers.

Radio Network House was badly damaged in the magnitude-6.3 February 22, 2011 quake and engineers ruled it unsafe.