CareVets Kilbirnie owner Nick Cooper says at this stage he does not know how many cats have survived or died in the blaze.
Emergency services were called to the fire at the two storey building on Mahora St in Kilbirnie at 11.50pm.
Cooper said cats that were pulled out of the blaze were given oxygen and taken to the after-hours clinic.
He said he did not know how many cats had survived the blaze or died as they had not been able to get into the building, and computers and paperwork were also inside.
There are two apartments above the vets but everyone got out safely.
Cooper said he and his staff had been on site since 3am on Sunday.
Fire and Emergency New Zealand central shift manager Murray Dunbar said eight appliances and four specialist support vehicles attended the fire, which was put out around 2.30am.
The blaze would be investigated, he said.
