A Newshub investigation has forced the Government to reveal a potential billion dollar cost blowout that has not been accounted for.

The problem is so big it has forced the chief executive of the Earthquake Commission (EQC) to publicly apologise to the hundreds of Christchurch homeowners affected.

Those people have unknowingly bought earthquake damaged homes, but are now left in a "no man's land" where nobody will pay for repairs.

Sid Miller, EQC chief executive, has seen the extent of the damage first hand. He went to Christchurch resident Cate Jones' house in response to Newshub's investigation, and saw the cracks for himself.

Ms Jones is just one example of a very big problem - one of hundreds of Christchurch people who brought a home only to later find out the damage hadn't been repaired properly.

Mr Miller admitted that if EQC accepts liability, the problem is about to cost the taxpayer hundreds of millions of dollars.

"Yes, we have a problem in that space," he told Newshub.

"Is it $100m? $200m? $300m? I don't know."