Auckland traffic delays 'a freak accident' - PM

Prime Minister John Key has ruled out an earlier construction date for a second harbour crossing in response to massive traffic jams which brought Auckland roads to a standstill on Saturday.

Mr Key said the traffic delays, which left some people stuck in congestion for four hours, were "a bit of a freak accident".

Watch: Auckland traffic chaos

He told reporters at his weekly press conference: "You think about the number of cars and motorbikes and trucks that travel over the Harbour Bridge and how infrequently it's beset by the sort of problems we saw on Saturday afternoon.

"For the most part it works well and traffic there is good."

He said an alternative harbour crossing over the Waitemata was required "at some point", but it was a big ticket item which would cost "billions and billions of dollars".

There was no plans to push the project forward.

"I don't think you just start building that tomorrow because there was an accident on Saturday afternoon," Mr Key said.

Mr Key reiterated that Government wanted the crossing to be a tunnel, not a second bridge.

The second harbour crossing is one of Government's top three transport infrastructure priorities in Auckland. It is likely to be constructed between 2025 and 2030 at a cost of between $3 billion and $4 billion.

Traffic build-up following the incident on the Harbour Bridge. Photo / Jason Dorday

One of the motorcycles involved in the incident. Photo / Victoria Young