The $10.3 million multi-storey facility boasts modern learning environments, open student-learning spaces, simulation wards and the latest technology.
Mr Key said Waiariki was a great example of making sure New Zealanders were being upskilled and given the chance to do well.
"Waiariki is a vitally important institution, it is doing extremely well and is going from strength to strength."
Waiariki chief executive, Professor Margaret Noble said the building had been finished to the highest quality.
"The new Health and Science Centre provides our community and students with state of the art facilities and an environment conducive to technological advancement in line with the innovative developments happening at Waiariki."
Professor Noble said the institute's academic staff and the architects spent "considerable time and effort designing a building that would suit the modern student's needs".
"It is a fit-to-purpose facility with a lot of flexibility.
"Nursing is our biggest degree programme and it is important to ensure our students are learning in an innovative environment which nurtures and breeds the necessary skills for today's working environment."
First year nursing students Lisa Mercer and Andrea Crengle said they felt lucky to be among the first students to utilise the new building.
"It's a fantastic resource and allows us to train in a more stimulating, realistic and practical environment," Ms Mercer said.
"Having resources such as a simulation room will be extremely beneficial to the quality of our qualification," Ms Crengle said.
