Twelve 54-tonne concrete beams were installed over the weekend at the Bayfair flyover for the Bay Link project.
New Zealand Transport Agency Waka Kotahi infrastructure delivery regional manager Jo Wilton says the 28m long beams - which were the "main structural element" of the State Highway Two flyover - were lifted into place by a 300-tonne crane.
Wilton said the flyover would take SH2 traffic over the Bayfair roundabout, separating the state highway from local traffic and create a safer environment.
The work was carried out on Friday and Saturday with overnight lane closures and detours in place from 7pm until 7am both days.
Wilton said construction would now continue on the flyover's remaining pier and the northern ramp of the flyover would "emerge out of the ground".