Auckland's Eastern Busway was opened this morning, with a dawn blessing at Panmure.
It will open to passengers on Sunday.
Transport Minister Michael Wood said people would make up to 30,000 trips on the service each day.
"With services every 5-10 minutes between Panmure and Pakuranga, we're expecting around 5000 people to use the busway during the morning peak and up to 30,000 passenger trips daily.
"We really encourage people to give the bus a go, and passengers will also get a chance to check out the 210m steel 'busway bridge' that crosses the Tamaki Estuary alongside the existing Panmure bridge," Wood said.
Wood said the project would be a "game-changer" for east Auckland which experiences bad congestion.
"People who live in east Auckland know the area has some of the highest traffic flows and worst congestion in the city.
"The dedicated bus lanes will be a game-changer, allowing commuters to link in with Auckland's rail network and once fully completed, get from Botany to the central city in 40 minutes.
The $1.4b project is being built in three stages. The first involved Panmure station and the surrounding upgrades, with the second stage being the first part of the busway from Panmure to Pakuranga. The third and final 5km stretch of the project between Pakuranga and Botany is currently in the design phase and is budgeted at $867m.
It will connect Botany, Pakuranga and the surrounding suburbs to the rail network in Panmure. When fully complete, it will be possible to travel by bus and train between Botany and Britomart in 40 minutes - 20 minutes quicker than now.
Auckland Mayor Phil Goff said the project would be a "massive improvement in access to frequent and reliable public transport in east Auckland".
"With government support and funding from the Regional Fuel Tax, we will now be able to move on to create the next stages of the busway through to Botany, further extending Aucklanders' access to world-class public transport throughout our region," Goff said.
The project is funded jointly by Waka Kotahi NZ Transport Agency, which picks up 41 per cent and Auckland Transport which picks up the rest.
The second stage of the busway was in doubt earlier this year after a funding wrangle between Auckland Council and the Waka Kotahi saw the timeline for stage two of the project pushed out from 2025 to 2027.
Following the decision to cancel the Auckland cycle bridge, the Government was able to bring the timeframe for completion forward.