The largest joint New Zealand defence force exercise in 15 years is underway in the central North Island.

About 1500 navy, air force and army personnel are expected to take part in Exercise Alam Halfa over the next week.

They will be joined by nearly 80 personnel from the US Army and the US Marine Corps Pacific forces.

A training scenario, in a high-combat setting, will require the troops to restore peace and transfer control of a fictional country back to law enforcement and democratic authorities.

Most of the exercise will take place in the Waiouru Military Training Area.

Military personnel had been scheduled to take part in a similar exercise in February and March last year, but this was cancelled as troops were mobilised to respond to the Christchurch earthquake.