Witness Lachlan Harris said the surfers were playing with the whale before it tossed them.
"It was a whale the size of a bus. I mean, it was 40 feet long - it was huge.
"They were playing and the whale was frolicking with them and having a lot of fun and sort of popping its head out.
"It just flicked its tail and some surfers were in the wrong [place] and the next thing you know a surfboard is flying in the air [and] swimmers are getting thrown out of the water. It was unbelievable."
Mr Harris told the Sydney Morning Herald at least 300 people were there to see the incident up close.
"Looking north along the sand, the whale was sort of behind them and they could see the whole thing. Everybody had their mobile phone cameras going off.
"It was just amazing. I mean there were people swimming laps of the beach and the whale was even inside them. It was that close to the beach."
- nzherald.co.nz