About 3000 customers have been affected by Air New Zealand's grounding of its ATR fleet, after hairline cracks were found in one plane during routine maintenance.
The airline has been carrying out inspections on Sunday on its 11 ATR aircraft, which are operated by its subsidiary Mount Cook.
The cracks were found around the cockpit windows of one plane during routine maintenance overnight in Christchurch.
Air New Zealand cancelled all ATR flights on Sunday, but the airline says alternative travel arrangements are being put in place.
Two ATR planes were returned to service between Christchurch and Rotorua and Auckland and Palmerston North later on Sunday.
Mount Cook's general manager Sarah Williamson says she expects to introduce more aircraft back into service later on Monday.
But disgruntled passengers say they were left in the dark over the airline's decision to ground the planes.
One passenger, who arrived from Australia, was meant to be travelling from Christchurch to Queenstown on Sunday.
She says she wishes the airline had contacted them earlier, so they could have made alternate plans to the six-hour bus ride it is offering.
An A320 aircraft has been brought in to provide some services between Christchurch and Dunedin and Christchurch and Wellington.
The 68 seat ATR planes have serviced 10 destinations for Mt Cook since 1999 and have an average age of about 11 years.
Air New Zealand grounds 11 planes . . .
Air New Zealand has grounded 11 planes for inspections after cracks were found around the cockpit windows of one aircraft.
The airline said its 11 ATR planes - the propeller driven 68-seaters operating regional services around the country - had all their services cancelled this morning after the cracks were discovered.
The planes are operated by Air New Zealand subsidiary Mt Cook Airlines.
A media statement said one aircraft in Queenstown had already been inspected, had passed, and was back in service.
Mt Cook general manager Sarah Williamson said alternative arrangements would be made for affected customers and other aircraft from the Air New Zealand fleet would be used.
"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."
The ATR-500 aircraft have been used by Mt Cook since 1999.
The airline said the planes were an average of 10.9 years old.
They service 10 destinations around New Zealand.