The Cambridge section of the Waikato Expressway has been officially opened – six months ahead of schedule.

The $250 million NZ Transport Agency project, stretching from the Tamahere Interchange to just south of Cambridge, has eight bridges, walking/cycling paths, artworks and 365,000 native and exotic plants along its length.

Transport Minister Simon Bridges officially opened the Cambridge section on Tuesday morning before a community open day on Tuesday afternoon. The road is expected to be open to traffic from Wednesday.

JASON DORDAY/Stuff.co.nz The Cambridge section of the Waikato Expressway was officially opened on Tuesday and the public will be able to use it for the first time from Wednesday. It runs between Tamahere to just south of Cambridge, passing over eight bridges, including the imposing Karapiro Gully Viaduct.

"There are four words - under time and under budget. They are like music to my ears ... they mean we can do other areas quicker," he said.

"It's not every day you get the chance to open a $250 million project and this is a significant project for a significant region."

Hundreds of people turned up to the community open day on Tuesday afternoon, where they had the opportunity to walk, bike, or bus the expressway before traffic takes it over.

Ascend Photography The sleek Peake Rd Bridge is one of eight new bridges making up part of the Cambridge section of the Waikato Expressway.

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Rototuna resident Jordan Smith travelled specifically to the event.

He travels through the area for work and has enjoyed watching the progress.

Ascend Photography The sleek Karapiro Viaduct is one of eight new bridges making up part of the Cambridge section of the Waikato Expressway.

"Because I don't come down here every day I have seen its stages and bigger changes being made, rather than going through it every day and not noticing it," he said.

His grandfather was a road engineer, so he has always had an interest in roading infrastructure.

He believes the $250 million was money well spent.

"It's a lot of money per kilometre but it needed to be. If it's not 100 per cent needed now then it will be in the future; it's silly to build a road after it is required."

Leamington resident Penny Pluck agreed.

"It's been all around us .. we've watched all the traffic jams," she laughed. "It's so cool that we have a main road. We've never had one like this, it's like what you see in Auckland.

"I grew up in this town so it's been really weird just watching the farms and roads being moved."

The project is one of seven sections of the $2.1 billion Waikato Expressway, a Road of National Significance identified by government as key to unlocking New Zealand's economic potential.

The 16 kilometre Cambridge section is the third part of the Waikato Expressway to be completed.