Concerns are being raised over the safety of the first floor of an inner-city gym after an engineer's report identified six months ago that parts of the concrete floor were crumbly and could collapse in an earthquake.

The outcome of an on-site inspection by engineers BCD Group obtained by the Herald said the first floor of the Les Mills building at 611 Victoria St in Hamilton needed urgent investigation and was at risk of collapsing in a quake if the concrete quality was found to be poor across the entire floor.

"Such an event could include catastrophic failure to the building and expose occupants to high levels of earthquake risk," BCD's report said.

Firth Concrete central material manager Paul Donoghue visited the site as part of BCD's appraisal.


Mr Donoghue believed the problem could be widespread. "It appears to be pretty old and poor-quality concrete that's causing it. And if you take a handful of the concrete it just crumbles in your hand."

Les Mills property consultant Blair Wolfgram said there had been a temporary repair job to the hole in the floor after the initial inspection and the landlord had reassured them the property was not earthquake-prone based on a 2010 seismic assessment.

"We were uncomfortable with this essentially and that's why we've gone out and looked for another site and we are looking to move in there in March ... We've got to hope there's no earthquake between now and March in Hamilton."

Les Mills is building a new $5 million facility at the former Mitsubishi site at 729-747 Victoria St.

Auckland-based landlord Allan Webster said he had no knowledge of the BCD report and confirmed no further investigations had been done since April. Mr Webster said a two-year-old assessment by engineering firm Stiles and Hooker found the building was not deemed high risk in an earthquake.