After eight years of construction beneath Tauranga Harbour, the Southern Pipeline is finally being completed today.

Project manager Chris Thomas said from the site this morning contractors were working on the final 40m of pipeline casing before it was expected to resurface at Matapihi peninsula at 10am.

It's a major moment for the $99 million project, which has been beset by delays and problems since construction started in Greerton in 2010.

The Southern Pipeline will redirect some of the city's wastewater to the treatment plant at Te Maunga. The new pipeline will relieve the burden currently on the Chapel St treatment plant, allowing the plant to improve its performance.

"There have been six cranes over there [at Memorial Park] over the past four days which are now packing up.

"There's an air of excitement at the site.

"There will be a celebration tonight, no doubt. It's a huge milestone for the contractors involved.

"There is an Australian drill which has an Australian team of people, and a local team as well. They have done an amazing job. It's been a surreal weekend."

Thomas said he had never seen so many people working so efficiently together on a project with so many parts to it.

Contractors have been operating in two 12-hour shifts in teams of 25.

Another product pipe was expected to be worked on over the next three weeks but it "will be less intense".

Tauranga City Council infrastructure manager Christine Jones said steel pipes began being thrust and pulled through a 1.6km-long drilled hole under the harbour from Memorial Park on Friday, supported by a line of cranes.

The pipes breached the 1km mark yesterday.

Jones said the harbour crossing was the riskiest part of the project.