NZ Transport Agency senior project manager Phil Dowsett says the section will be completed by Christmas.
It was the final section to be constructed because the space underneath had served as a launching pad for both assembling the bridge's steel girders and pushing them by hydraulic means along the span to where they were fitted in place.
The southern abutment would then able to be completed, Mr Dowsett said.
Workers would complete the embankment along the river bank before the final span was put in place.