Health NZ can not put a timeframe on the replacement of Auckland Hospital's flea-infested carpet, with one former project manager warning it could take decades.

Staff at Auckland Hospital have made hundreds of reports about fleas and other insects in the past year.

HNZ's group director of operations for Auckland Dr Michael Shepherd previously told RNZ that work to replace carpeted areas with vinyl flooring was underway across its facilities, but this had to be carefully planned to minimise disruption, as it often required clinical services to be temporarily relocated.

"This work is scheduled for periods when suitable decant space is available, allowing services to be temporarily relocated while minimising disruption to patient care," he told RNZ on Wednesday.

But a previous senior project manager for Auckland Hospital - who RNZ has agreed not to name - said about 40 wards and departments had carpeted hallways, with the carpet installed in 2003 when the building opened.

They said at the pace work was going, it would take more than four decades to complete.

On install, the lifespan of the carpet was five to 10 years, they said - meaning it was well overdue to be replaced - and fleas had emerged as a major issue in 2014.

Health NZ could not put a date on the programme's completion, and did not respond to these specific claims.

"While we do have decant space available at times when hospital occupancy is lower, particularly outside peak winter periods, capacity requirements vary throughout the year," Shepherd said.

"As a result, the programme remains flexible and is planned around the operational needs of the hospital.

"We remain committed to maintaining safe, clean, and well-maintained facilities for our patients, whānau and staff."