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.