A whale watcher has captured spectacular footage of a pod of about 1000 dolphins fleeing an ambush by orcas in waters off California.

Michael Sack, co-owner of Sanctuary Cruises, said there had been an “almost unprecedented” run of daily orca sightings in April.

He said he “just happened to be in the right spot at the right time” to witness the ambush by a group of eight to 10 orcas, who usually attack gray whale mother and calf pairs.

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“They’re right under here waiting to ambush these common dolphins coming our way. So in a second you’re going to see all of these common dolphins take off like you’ve never seen before,” he says in the video.

One dolphin is then killed by an orca, sparking what Mr Sack calls a “stampede”.

“Look at them all! They’re running right now. This is a pretty epic encounter I just had,” he says.

Mr Sack later wrote on YouTube that it was “very rare that everything comes together and we’re able to document these types of encounters”.

“We know it happens regularly with the common dolphins. But there’s rarely someone there with their video camera focused and waiting for it to happen. Incredible morning on The Monterey Bay for me,” he said.