Most of coastal Papamoa and Mount Maunganui slept through the November 14 earthquake and tsunami warnings - but thousands across the Coromandel Peninsula were evacuating their homes.
Thames Coromandel District Council area manager for Whangamata, Tairua and Pauanui Garry Towler said he sounded the sirens at 1.45am on Monday.
"Within 20 minutes, every community which had a siren on the Coromandel Peninsula had evacuated to higher ground."
About 25 sirens were placed along the peninsula about 12 years ago.
It was the first time for many people that a siren had been sounded during a serious event, he said.
Mr Towler said thousands of people evacuated through the night.
"It was a credible threat."
He was encouraging locals to now download the Red Cross Hazards phone app.
Mr Towler said locals could not rely entirely on the sirens.
"A number of communities still didn't have sirens and houses have double glazing, or people simply did not hear the siren or had hearing impediments."
If people felt an earthquake of more than a minute or were knocked off their feet they should self evacuate, he said.
"People should not rely on Civil Defence staff to save their lives."
People should also check the Red Cross phone app, listen to the radio or television and check social media for warnings and what to do.
"If you hear a siren you should seek further advice before you evacuate, find out what is going on."
Whangamata resident Jan Findlay said she thought she was dreaming when she heard the siren go off.
"I flew out of bed and put some warm clothes on, I grabbed some vitals in a box and took off in my car.
"I was pretty motivated to move. I grabbed a picture of my father when he was a child but nothing else. I didn't bother with food. I knew I could go three days without it."
She beeped her car horn through her neighbourhood and drove up The Drive towards Pacific Heights and waited with other residents, she said.
"I know the Kermadec Trench and White Island are our biggest threats here in Whangamata and we didn't know where the earthquake was at the time."
She was surprised at the number of elderly people who had made it up the hill.
"It seems there were quite a few people still awake and aware an earthquake had taken place."
Another resident Chris Cotter said it took her a few seconds to register what was happened when she woke up to the siren and headed up the hill.
"Everybody was very orderly but the hill was chocka."
Ms Cotter said she was more worried that she did not really know what was going on rather being scared for her safety.