It could be the piles of shattered glass, broken maso' />

It is hard to judge what is the most disturbing sight in central Christchurch's "red zone".

It could be the piles of shattered glass, broken masonry, wood and metal from buildings that collapsed in the devastating February earthquake. It could be the large empty spaces where familiar multistorey buildings and landmarks once stood. Or it could be those damaged high-rise buildings that are still standing but leaning precariously as you walk beneath them.

Intersections that used to be unmistakable are now barely recognisable. Where there were constant queues of traffic and human activity are now deserted streets, empty but for the odd construction vehicle or workman in a high-visibility vest.

Almost three months after the quake, some of the debris has been cleared away, but the area still seems a long way from being the hub of the city's activity it once was.

"Every time I come in here, you get quite affected by it because it's a huge, daunting task," says Warwick Isaacs, demolition manager for the Canterbury Earthquake Recovery Authority (Cera) and an escort on a media tour of the cordoned-off central city zone yesterday.

"And the task isn't just around buildings coming down. It's about the impact on the people who own those buildings, and the tenants inside those buildings, whose lives are irrevocably changed because of the damage in here."

Add to that the fact that this area is still changing as every decent aftershock brings more damage.

"The land is still settling. Whether it has settled entirely or not, I don't know," Mr Isaacs says.

"But certainly buildings are still moving on the earth. I'm sure everyone [working in the red zone] is on edge to a certain degree."

As the tour into the red zone begins, our guide warns us we are effectively going into a big construction site. He says the greatest risk in this area is masonry that could still fall from damaged buildings.

"As a general rule, the centre of the road is the safest place to be."

As you travel through the eerie streets, avoiding collapsed building facades and pavements buckled and covered in glass, some sights are more powerful than others.

We get within 20m of the base of the 26-storey Hotel Grand Chancellor, which is noticeably on a lean and appears to be resting against a smaller hotel next to it. It's un-nerving being so close when the risk of an aftershock is ever-present.

Mr Isaacs says he has been up to the 12th floor of the hotel since the February quake and "it's quite eerie and quite spooky to be up there, to be honest".

Then there is the site of the former Canterbury Television building, where 116 people are believed to have died.

All that remains of the six-storey building are the broken concrete base of the lift shaft and piles of debris.

Cera's interim chief executive, John Ombler, said a lot of the initial demolition of very unsafe buildings had already take place.

"Now we are getting into the more methodical business of working with owners and insurers to progressively pull down everything that needs to be pulled down. And that's going to take a long time.

"We are talking about many hundreds of buildings."

Mr Ombler said getting central Christchurch back to normality again would take years rather than months.