A pod of orca swimming and chasing stingrays in Auckland harbour caught the attention of beach-goers on Saturday morning.

Tracey Thornton spotted the whales about 300m offshore while walking her dog at Mission Bay.

Ms Thornton, a wildlife photographer who had just returned from Alaska, raced home to grab a camera with a large lens and for 90 minutes tracked the whales east past St Heliers and onto the Tamaki River.

Later they were also photographed by Rob and Gin Mager at Bucklands Beach.

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Ms Thornton estimated the pod featured 8 to 10 whales and believes they were chasing stingrays.

"They move very fast. When they're going down the harbour, they're in feeding mode, they go after the abundant stingrays.

"Stingrays go to the bottom, so when they see them, they will grab stingrays' tails and flip them around to avoid the barbs."

Despite the churning ocean, the orcas weren't hard to see. "Their big dorsal fins, up to a metre high, were very distinguishable. They're quite active in the water and when they're going after stingrays they flick their tails up to get momentum to dive."

On the east side of the Tamaki estuary, Bucklands Beach residents in their dressing gowns and pyjamas gathered on The Parade to watch the pod around 9am. Gin and Rob Mager watched from their deck. "When they were feeding, quite a big one was slapping its tail around, struggling with a stingray," Gin said. "It looked spectacular."

The couple see orca from their deck sometimes three times a year.

The playful orca came as close as one metre to the shore and were unafraid of boats, Rob said.

"They go underwater and blow bubbles on the ground to get the stingrays off the ground. We could see what he was doing, to dislodge the rays. Stingrays hold onto the ground, so orca put their tail and bubbles down to make the stingray release.

"We have seen them throwing them in the air [in the past], like a cat with a mouse."

DOC describes orcas as the most widely-distributed mammal on earth.

Sightings should be reported to the 0800 DOCHOT hotline.