Prime Minister John Key has turned the first piece of turf to mark the start of construction of the new Kopu Bridge near Thames.
The bridge will replace the existing one-lane bridge over the Waihou River on State Highway 25, which has been the scene of huge traffic delays during holiday periods as motorists from Auckland head to the Coromandel Peninsula.
The original bridge, built in 1927, does not meet modern design and construction standards and is not likely to withstand a severe earthquake.
A new bridge has been promised for many years and was included in the Government's new infrastruture package announced in February, which brought its construction forward by two years.
The budget for the two-lane bridge is $47 million. It is expected to be completed in 2012.
Thames-Coromandel Mayor Philippa Barriball says the new bridge will provide an economic boom for the region.
Ms Barriball says costs associated with delays on the existing one-lane bridge are estimated at $92 million a year.