The Department of Conservation (DOC) has called the death "unusual" and said it was at the scene at a beach north of Waimairi along with local iwi and members of Project Jonah.
DOC Mahaanui Operations Manager Andy Thompson said a member of the public alerted DOC to the situation, and due to "challenging" sea conditions the body was unlikely to be moved before Friday morning's low tide.
Staff remained at the beach overnight, Thompson said.
"We understand the orca was dead when it was spotted by a member of the public who alerted us. We ask that the public stay away to give staff and iwi the space to respond to this incident."
A vet pathologist would fly down to Christchurch from Massey University on Friday, Thompson said, to perform a necropsy on the orca to try and figure out how the animal had died.
"Appropriate tikanga will be followed and the orca will then be buried on the beach," he said.
"It's unusual for an adult orca to be found dead in the shallows like this and in good condition. Our national marine team are very keen to find out why the animal has passed away."
