Air New Zealand is inspecting its ATR fleet after hairline cracks were found around the cockpit windows of one of its planes.

The cracks were found during a routine inspection of the 68-seat aircraft in Christchurch, Air New Zealand said in a statement.

The remaining 10 aircraft in the ATR fleet, all operated by Mount Cook Airlines, were currently being inspected.

Inspections on one aircraft in Queenstown had found that it met all required operational standards and it was now back in service.

Mt Cook Airlines General Manager Sarah Williamson said services were cancelled this morning while checks were undertaken.

Alternative arrangements would be made for affected customers and other Air New Zealand aircrafts would likely be utilised.

"We apologise to customers for the inevitable inconvenience caused by undertaking a full check of our fleet. However, the safety of our customers, our staff and our aircraft is paramount and non-negotiable for the airline," Ms Williamson said.

Customers travelling with Mount Cook were advised to check flight arrivals and departures on Air New Zealand's website: www.airnewzealand.co.nz