"They're in a dangerous condition."
Mr Maclean said it was not yet known whether those houses could ever be occupied again.
"That is the big question. There are some schools of thought that remedial work could be done to the top of the slip, but obviously that's got to be a decision made by EQC and the insurers and the council as well."
Mr Maclean said building inspectors and geotechnical engineers were this morning checking the ground and foundations at the evacuated properties.
"We're obviously looking at all the properties with a view to hopefully letting them back into them."
Emergency accommodation had been provided to about 30 people until Tuesday.
The council was hoping to let residents know before then whether they could return to their properties.
Mr Maclean said many of the residents were renters, so the council had been in touch with Housing New Zealand and the council's own social housing unit.
"If the houses are unusable, we're going to have to find them alternative rental accommodation."
Mr Maclean dismissed suggestions the slip had been caused by a burst water main.
He said a burst main had been reported on Friday and the council had inspected the street then, but no evidence of a burst main had been found.
Mr Maclean said a sewer main and a stormwater main which ran across the slope below the houses had been destroyed in the slip.
The sewer main had been temporarily reconnected, but sewage remained an environmental hazard in the cordoned off area around the slip.