The Transport Agency says Thursday marks the beginning of New Zealand's largest motorway project.
The $2 billion Waterview connection in Auckland will complete the north-western motorway corridor, providing an alternative route from north to south.
Prime Minister John Key started the biggest and first phase of the project, two 2.4km tunnels, by turning the first sod.
Work on the tunnels begins next year and the project is expected to be finished by 2016.