A Waikato Hospital worker was accosted as she walked to her car after working a late shift on Wednesday night.
It is the second attack at the hospital recently after a the attempted sexual assault of a female health professional, who was visiting the hospital, as she walked back to her car on Boxing Day.
Police said the latest incident involved an attempted robbery of a 49-year- old.
Detective William Loughrin, of the Hamilton CIB, said three men approached the woman as she left work and walked to her car, which was parked in a car park adjacent to Waikato Hospital's helipad, shortly nafter midnight.
One of the men, described as young Maori man of fat build, accosted the woman and demanded she give him her handbag.
She initially refused, but then dropped her bag as a distraction so she could get to her car and lock herself in it.
She started beeping her horn to draw attention to the attack, with two of the group fleeing.
But the teen who initially attempted to rob her continued to threaten her as she started her car and began to leave.
Mr Loughrin said the woman was terrified by the ordeal.
''We would ask that anyone who witnessed this event take place or who may have information on the identities of the attacker to come forward,'' he said.
Police have released an image of one of the men they want to speak to about the attack.
''But more importantly, we're asking that the two males initially involved in the incident to come forward and make contact with Police.''
Anyone with information can call the Hamilton Central Police Station on 07 834 9413, Mr Loughrin on 027 704 8589 or leave information anonymously with Crimestoppers on 0800 555111.
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