There were cracks around the cockpit windows of an Air New Zealand plane, the airline found on Sunday, resulting in the grounding of 11 planes on the same day.

The cracks were spotted during routine maintenance check in Christchurch.

The propeller driven 68-seater ATR planes, otherwise called turboprops, carry passengers to around 10 destinations in the country.

The planes are operated by Air New Zealand subsidiary Mt Cook Airlines.

All the services were cancelled Sunday morning right after the cracks were discovered.

Mt Cook general manager Sarah Williamson said the airline will take care of alternative arrangements for affected passengers, such as the use of other Air NZ aircraft. This alternative will allow Mt. Cook to operate with about two-thirds of its normal seat capacity today (Monday).

"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."

Fairfax NZ news reported the ATR-500 planes have been used by Mt Cook since 1999, with the planes averaging 10.9 years in service.

Air NZ released a media statement saying one aircraft in Queenstown had already been inspected, had passed, and was back in service.

An estimated 3000 passengers have been affected by the grounding, said Ms. Williamson in a statement.