Just one concrete panel falling from an apartment building near Auckland's SkyTower has shut down an entire city block to traffic for at least the whole weekend.

Photo: RNZ / Sarah Robson

Not only that, the council and the owners of apartments on the corner of Nelson St and Victoria St West have known about the problem since 2012.

Some seven years ago, the leaks and cracks started appearing in the cladding of the Victopia apartment building.

And, despite being the subject of the country's largest-ever leaky building claim of $40 million, bits of the building are still falling off.

A concrete panel, weighing an estimated 40kg came crashing down from the 13th floor yesterday, and engineers today found many more panels were coming loose.

Repair work was already underway when the panel fell so the area below was cordoned off, otherwise pedestrians on the sidewalk below could have been in real trouble.

Ian Harris from the Victopia body corporate has been handling all media inquiries today.

"I wouldn't expect it be completed until very late this weekend or early on Monday. We've got two or three teams of people which we're calling in to get the work done," he said.

"There's two cranes that will be in place, and a couple of abseil teams working to do the repairs on the side of the building."

Engineers were today hoisted up the side of the building in a crane basket and checked the other panels on the building.

About 40 or so red crosses mark panels they suspect are loose and need reinforcement.

Teams plan to fix additional wooden panels over the top before securing the exterior with a net.

Traffic has been backed up on Nelson St and either side of the cordons on Victoria St for much of the day, and Auckland Transport spokesperson Mark Hannan said it's going to stay busy on the roads.

"We are managing the traffic signals but the traffic is still very busy in the area. And we have six bus stops that have had to be closed.

"We expect it will be busy again this afternoon. It was certainly busy this morning, but Friday does seem to be bit quieter and the afternoon peak is spread out over a longer period. But I would certainly try to avoid that Nelson St and Victoria St if I possibly could."

Lawyer Tim Rainey gave advice to apartment owners when they were lodging the biggest-ever leaky building claim over the Victopia apartments.

Photo: RNZ / Sarah Robson

"Mostly the issues with the cladding were discovered because there were found to be leaks and weather tightness issues with the building. There were cracks in the joins between the cladding, which was allowing water to get into the structure of the building," he said.

"There was also pressure on those panels because of differential movement between the different elements of the building."

A confidential settlement was reached before the case got to trial and the company that constructed Victopia and other leaky buildings, Brookfield Multiplex, went into voluntary liquidation.

"They were facing many tens of millions of dollars - hundreds of millions of dollars - in fines and rather than fronting up, they closed down the New Zealand operation and scurried back to Australia," Mr Rainey said.

He was bewildered that the building was still having problems so many years on.

"What this really highlights is that building is so complicated and dependent upon people doing their jobs properly, from the people who design the building, the people who build it, and the people who inspect it. There are so many ways that it can go wrong.

"I don't know what the cause of this panel failure was, but what it does highlight is that we still have problems with the quality of construction in New Zealand, right down to this day."

Lucy Xia is a former Victopia resident who was there during the leaky building palaver.

"It was many years ago, a piece of cladding fell from the building on to Nelson St. And that was how they discovered that there were issues with the building and started investigating. And then they came to the conclusion that outbuilding was leaking and needed remedial work."

However, she said it had been a good place to live.

Auckland Mayor Phil Goff said steps need to be taken to deal with the risk of further panels falling and he hoped this could be done as quickly as possible.

"Council and AT staff are working with the building owners to ensure work is done to the proper standard as fast as possible. I expect council officers to be asking hard questions of the building owner about the safety of the panels on this building."

Victoria St West remains closed between Hobson and Nelson Sts; Nelson St is closed between Victoria and Fanshawe Sts; and Victoria St West's east-bound lane is closed as you head towards Nelson St.