Auckland Transport was urged to have unstable land fixed several months before two slips appeared in Birkenhead.

Two sections of a carpark on Rawene Road were torn away by separate slips late last year.

It has now been revealed engineers recommended two options to fix the unstable land in 2015, or at a minimum, install an early warning system to monitor the stability of the land.

Northcote MP Jonathan Coleman says Auckland Transport didn't act on any of the recommendations.

"They need to explain why they did nothing and I am extremely disappointed and I think you will find there is a lot of angry people in Birkenhead."

He says Auckland Transport has let the community down.

"Auckland Transport have just ignored what was a looming problem, they have ignored the professional advice."

The slips could now cost around $24 million to fix.