Christchurch's second post-earthquake building implosion has gone off with a bang - a "surprisingly loud" bang at that.

The former police station, badly damaged by the 2011 quake, has been demolished.

At bang on 5pm several long sirens sounded, before the building fell to the ground in around 8 seconds.

Newstalk ZB's Emily Murphy was there and said it was very exciting for all those gathered to watch.

"The public definitely erupted in a big cheer once it was complete. The ground was shaking a bit as it was demolished."

As the building fell, it leaned off to one side, sparking concerns over whether everything went according to plan.

But demolition company Ceres NZ spokesman Bernie de Vere is happy with the implosion.

"A few questions have been asked about why the building is leaning the way it is, it's exactly the way it was planned. Everything has gone according to our planning and the building is sitting in it's own footprint."

Field operations manager Ray Zukowski said the building was incredibly rigid, so getting it down to the ground was no easy task.

"We charged about 185 holes, and we loaded about 50-55 kg of high explosives into the building."

Emily Murphy said locals who witnessed the 2012 Newstalk ZB building implosion feel today's wide scale demolition was very similar and just as loud.

And some Christchurch residents may have be caught unaware by the blast.

Shannon Hardy was at her home, located several kilometres away from the former station.

"It was really loud and it caught me off guard, I forgot it was happening."