It transpired a group of youths, up to seven of them, had brought about the arrival of the guard.
The youths had been going to the library and causing problems for staff and other visitors for the past few months and it had been decided to issue them formally with four-week bans .
"However, this did not work," Napier City Council communications manager Robyn McLean said.
As a result, formal trespass notices were issued and over the recent school holidays a security officer from First Security Guard Services had taken up station "to ensure the trespass notices were not breached".
Ms McLean said the officer would remain at the library until the end of the week when it would close for four weeks for redevelopment work.
There had been no decision at this stage upon whether the guard would return after that time.
The attraction of the library for the youths appeared to be the internet access available.
One person who remarked online through the council's Napier News Facebook site about the activities of the group said there had been up to seven teenage boys involved and that they had abused staff who asked them to leave.
Ms McLean said although getting police to arrive to clear the trespassers off was the first option it was realised there were times when their resources were stretched.
"So hiring security to enforce the trespass was our only option," she said.
Another visitor to the Facebook site, Josh Perks, said while it was sad to see security staff needing to be put in place he said it made "perfect sense" in this case.
"I don't think library staff should be required to enforce a trespass notice."
Maureen Hannah thanked the council for taking the unusual stance - "for keeping us safe".