"People [were] saying, evacuate as it's a tsunami warning," he said.
"The manager was on a loud haler asking people to leave and go to Wahi," he said.
But Henderson and his children aged 10, 13 and 16, got into three cars and fled to high ground.
"Boom, off we run back to camp and pack up the kids and off we go, along with the town," he said.
Henderson said it was only when they reached Waihi that a police officer said it was a false alarm.
"I am puzzled as to why we did not get a text alert even if it was a false alarm," he said.
Despite the false alarm, Henderson said it was "just a little blip" during their visit to the Bay and they would stay at the campsite until Thursday.
Fire and Emergency chief Executive Rhys Jones has apologised for the error. He could not say if it was human or a technical error at this stage, but they would be investigating further.
The Bay of Plenty Civil Defence said on its Facebook page that had there been a genuine risk of a tsunami approaching, or other emergency situation, they would have used all avenues to alert people in the area.
Civil Defence is also investigating exactly what caused the sirens to go off.
A statement released by fire authorities said: "We are focused on working alongside our partner agencies to find out what caused these sirens to activate.
"The activation was an error and there was no danger to the public."
Tauranga mayor Tenby Powell said the first he knew about the false tsunami alert was when he read about it this morning.
"I didn't hear the sirens or get a text so I had no idea and I know lots of other people didn't either," he said.
"I know it's been very concerning and disturbing for many of our residents, particularly those aged 65-plus, many of whom rely on the sirens to know to go to higher ground if they can because they don't have cellphones. "
Powell said he was also deeply concerned this had happened.
"I only hope this technical glitch has been fixed and it never happens again," he said.
Recently taking over as chair of the Bay of Plenty Civil Defense & Emergency Management Group, Powell said he will be asking further questions to really understand the background as to what happened.
"I also want to satisfy myself that if the sirens did go off for real that people know what they need to do."
Western Bay of Plenty mayor Garry Webber said he and his wife, who live about 200 metres from the Ōmokoroa Fire Station, heard the sirens go off about 9pm.
Webber said he initially thought because they did not get a text it was some kind of drill or exercise and because they live on higher ground stayed put.
"Firstly, we know the system works, but secondly it is a little bit concerning no one knows what triggered it going off," he said.
"False alarms do not help anyone, especially after there has been a lot of effort in this district to help educate the community on how to react in the event of real tsunami evacuation warning."
Webber said he hoped the outcome of the Fire and Emergency New Zealand and Civil Defence's investigation clarified what went wrong so never happens again.
