These volunteer first responders trained for a mass-casualty event for years. On Sunday, their worst fears came true.

By day, Davi Smith is a financial consultant.

But on Sunday night he was an emergency medical first responder, treating patients within minutes of the Bondi Beach attack.

"It was obscene. Kids were running around looking for parents ... that was the best situation," Smith said.

"At worst, we had obviously deceased straight as we arrived, covered, and then we had critical patients that we had to triage." 

Smith is among a group of Bondi volunteers with charity Community Health Support (CHS).

The highly trained local team, which includes doctors, nurses, paramedics, and advanced first responders, has been training for a mass casualty event for more than two years.

Before the Bondi attack their preparations may have seemed extreme to some.

But for CHS, whose volunteers have strong ties to Sydney's eastern suburbs Jewish community, they knew they needed to be prepared for the unthinkable.

"That's what we're used to, to being on scene in many, many cases before an ambulance arrives, and we weren't unprepared for this type of scenario, unfortunately, but we knew what we needed to do, triage it, and go through the protocols and started to treat the patients," CHS executive director Jesse Lenn said.

The not-for-profit organisation was co-founded by Lenn four years ago.

Today, they have 120 volunteers and several full-time staff who are on call 24/7.

Their presence at the North Bondi parkland when the guns fell silent undoubtedly prevented more lives being lost.

For more information about CHS, visit their website.