The group, who had caught a bus to Bronte Beach in Sydney, ignored guidance to enter the water after hours before finding themselves in trouble on Tuesday evening.
Members of the local surf rescue club had just finished a Pilates class nearby and were able to respond when it emerged the swimmers were struggling.
In a message posted on Instagram, the Bronte Surf Life Saving Club said: "A fantastic mass rescue tonight at 8pm by a bunch of Bronte Members...
"Fortunately, we had 20 people just finishing their weekly Pilates class with Harries when this occurred and they were able to quickly grab gear and avert a mass drowning."
Anthony 'Harries' Carroll told Yahoo News 7 that Bronte Beach - located south-east of central Sydney - is one of the most dangerous beaches in Australia.
He added: "A couple of them had gone completely under
"I've been in the game 23 years and when you see that kind of thing, you just know you just need to go."
Surfers nearby helped keep members of the group afloat until they could be rescued using flotation boards.
The Club's statement continued: "When Harries and James got there, four of the eight were basically underwater, and very lucky to be saved.
"When will people learn that swimming at 8pm is a stupid idea, especially when not strong swimmers?"
Founded in Sydney by Brian and Bobbie Houston during the 1980s, Hillsong Church has grown to become a global church movement.
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