A second man chimed in saying he got a "real fright" when he stumbled upon a skull while out walking to collect rubbish on the beach.
"Saw the shining white in the sand, brushed it away, saw teeth! I freaked out, thought it must be an ancient Māori skull, called the cops, they came and had a look," he wrote.
Their conclusion: plastic and fake.
"They thought it was a hell of a joke! But they got to come to the beach on a sunny day so all sweet."
It seems the phoney skulls were planted weeks ago.
"I found one couple weeks ago down the beach at the waterfall," a man wrote.
A dad out with his son commented how he too had suffered a fright when the pair discovered one a few weeks back.
His sharp-eyed son didn't think it was real because of the shine – like it had been painted.
Some users pondered whether the spooky season had inspired the antics fit for Halloween.
However, the "idiotic behaviour" came as a concern to Heritage New Zealand Pouhere Taonga Northland manager Bill Edwards.
"Heritage New Zealand Pouhere Taonga has not been directly involved with reported prank burials and is very concerned that some individuals may be indulging in this behaviour."
"People carrying out prank burials - even with fake remains - should think about what they are doing to the emotional state of others, and stop this idiotic behaviour."
Edwards said human remains were not something "to be taken lightly or mistreated" as they elicited "strong emotions" from people connected to them.
"Human remains need to be treated with the highest level of respect - as you would expect."
Iwi representative Ric Parore (Ngāti Kuihi) believed some people may have had too much time on their hands during alert level 3.
He said when bones were discovered an archaeologist was often called in to examine them to determine the history behind the remains – alongside police and local kaumātua.
"I think any discovery has to be treated as genuine until we know better but in this case, it does turn out to be a waste of time for police," Parore said.
Archaeologists first examine whether the bones are human or animal, before determining if they are recent or historical.
Clues such as wear on teeth from eating fern root and the manner of burial often indicate bones are older.
Any recent bones warrant a police investigation.
While stumbling across genuine human bones/kōiwi on Northland's coastline may seem rare, it does happen.
More than a week ago, a member of the public found a human jawbone on the tide line in Ngawai Bay close to Helena Bay.
They were deemed to be historic before being taken to high ground and buried. A kaumātua blessed the kōiwi on the beach and later performed a karakia at the burial site.
Aerial view of the Bream Head Scenic Reserve in Whangārei Heads where the bone was found. Photo / NZME
In February, a Bream Head Scenic Reserve ranger chanced upon a kōiwi – part of the reserve's rich archaeological landscape due to more than 500 years of Māori occupation.
Two chance discoveries of human bones occurred last year in the Far North.
A Northland family walking around the base of Taratara Maunga, near Kaeo, found bones and skulls tucked inside rocks in June.
And five months earlier, a Whangārei couple holidaying in Russell unearthed around 20 bones making up a nearly intact human skeleton at Long Beach.
Edwards said occasionally kōiwi were uncovered in Northland and nationwide by weather, erosion, and earthworks.
"For every one of us alive around the world, there have been many people who have gone before us and who have been buried in urupā, cemeteries and many other different places - so it's no surprise kōiwi turn up from time to time in New Zealand."
He said tidal surges and erosion linked to climate change had exposed human remains, in particular those buried in coastal areas.
People who discover kōiwi should call either police or Heritage New Zealand Pouhere Taonga, who will then contact local iwi and hapū to ensure correct tikanga is followed.
Edwards encouraged people to take a picture of what they've found and the general environment to help provide broader context and record exact locations.
"If bones are found eroding out of the ground the best thing is to leave them alone or perhaps cover them with sand or soil if that's practical, then mark the spot so they can followed up later."
Bones found on the beach near the tide can be moved towards any grass area above the high tide zone, Edwards said.
"Cover them with something like a tarp or rug and mark the spot where they have been placed."
