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Twenty five people have been asked to remove gang regalia since the ban came into force three weeks ago, Waikato DHB security manager Dean Ria said.
"This has been at a time when we've had both Black Power and Mongrel Mob members at Waikato Hospital visiting fellow gang members," he told the Waikato Times.
"Nursing staff have been very appreciative of the rule which allows them to do their jobs without intimidation."
The ban followed an incident where a patient, who had been hit in the head with a hammer, arrived with "a heap of support people with him" and extra security staff had to be called in.
Mr Ria said security would also clamp down on unauthorised visitors and hawkers at DHB sites.