Panicked Waihī Beach residents evacuated on Sunday night, believing there was a tsunami warning, after a wave of sirens sounded across the Bay of Plenty.
Civil Defence and Waikato police later confirmed there was no tsunami warning for the area and said the sirens were a false alarm.
Civil Defence was working to get a better understanding on what had happened, the spokesman said.
Civil Defence later sent a text out to those in the area that Fire and Emergency had reported a fault in their siren system.
An evacuee told the Herald she and her family were staying at Waihī Beach when an alarm began to ring out.
"A siren started and we were wondering what it was, and then someone on loud speakers said we needed to evacuate as there was a tsunami," she said.
Sirens were also heard in Mount Maunganui, Te Puke and Ōmokoroa.
Waikato police said they were aware sirens were ringing across the east coast of the North Island.
"We have spoken with [Civil Defence] National Emergency Management Agency staff, who believe this is due to a technical fault," a spokesperson said.
Technicians were looking into the problem.
Tauranga City Council shared a post on Facebook saying it was aware sirens had been sounding but there was no national warning for a tsunami.
Witnesses said cars filled with panicked people were streaming out of Waihi Beach and local Facebook group pages were flooded with concerned comments.
"We all got new evacuation plans last week," commented one in a thread.
Te Puke Fire Brigade said the siren was confirmed to be a system fault and that Fire and Emergency would be investigating the matter.
The 19-year-old disappeared without her wallet or mobile phone.