New Zealand Transport Agency (NZTA) senior project manager Phil Dowsett said about 35 people were working on the 250m, two-lane curving structure.
The first of five piers was completed last week, and drilling for the second was now under way.
Mr Dowsett said work on the abutment anchoring the bridge to the southern side of the Kawarau River was nearly complete. Piling for the abutment on the northern bank had yet to begin and the present focus of activity was extending the temporary "trestle" platform above the river from the northern bank, to allow drilling for the third pier to start.
NZTA announced last month the project’s forecast completion date had been pushed back from next June until December.
Mr Dowsett said early forecasts had proved "optimistic".
"The rock’s proved to be particularly hard to drill out and that’s been more time consuming.
"We had extensive geotechnical investigation before we started, but when they came to actually break rock out, they found it harder than expected."
Drilling for the second pier — the deepest, at 11m — had to pass through "fracture zones" to the solid schist rock beneath.
"It needs to go that deep because it’s got to generate enough strength to resist earthquakes.
"Also, the bridge is on a curve, so there’s a lot of torsion in the deck and a lot of strain on those piers, so they’ve got to be very well founded in solid rock."
The first horizontal beams spanning the piers would begin to be jacked into place next autumn.
The bridge was now expected to open for two-way traffic before Christmas next year, he said.
Additional work such as landscaping, refurbishment of the old bridge and the connection of services would extend into early 2018.
