These are precast segments of the lining of the tunnel of State Highway 20, currently under construction. Each is 2 metres wide, weighs about 10 ton and 10 of them form a ring supporting the 14 metres wide tunnel. In all, about 24,000 of them have been cast in a purpose-built facility in East Tamaki, and here they wait at the southern tunnel approach to be transported to the Tunnel Boring Machine (called Alice). You will, of course, have done some fast and furious mental arithmetic, figuring that this yields about 2.4km of double tunnel.
(The segments arrive by road in sets of three, carefully numbered.)
You can watch a video of the casting process here.