About 50 killer whales were spotted in the waters off Botany Bay yesterday, July 12.
Photos of the incredible sight were posted on Go Whale Watching Sydney on Facebook.
Whale watchers on the boat tour about six nautical miles out to sea found themselves surrounded by at least 50 Orca whales from different pods.
The whales are believed to be type c Orcas – the smallest type, and are usually seen in the Ross Sea – a deep bay of the Southern Ocean in Antarctica.
They are known to migrate long distances but are not usually seen this far north and this close to shore.
Orcas are one of the most powerful predators, and are known to feast on sharks and seals.
The Go Whale Watching Sydney Facebook page posted it had not seen such a sight in 15 years.
Several humpback whales were also splashing around at the same time, appearing to harass the whales, whale watchers said.