One of the 12 nationally significant clusters in New Zealand, it involves 16 people who have tested positive for Covid-19, comprising up to 10 Hawke's Bay people - four tour guides or bus drivers, the six linked to the rest home, and six New Zealand passengers from the liner.
Ardern told a daily Covid-19 media conference in Wellington she has asked Attorney General David Parker to seek legal advice on whether the Ruby Princess and its operators had fulfilled all legal obligations.
The Prime Minister said that "of course" the obligation on the cruise company was to ensure no unwell person disembarked in the circumstances that were developing.
In relation to the Napier call, she said: "I have been advised that those assurances were directly sought by the Medical Officer of Health from the captain directly before individuals disembarked."
Napier Mayor Kirsten Wise reiterated on Tuesday that neither the City Council nor Napier Port would have had any authority to prevent the Ruby Princess berthing in Napier last month. Such authority of the port company, majority-owned by the Hawke's Bay Regional Council, related to whether ships could berth in certain weather conditions.
Wise said she had seen social media posts and had received a small number of emails suggesting the Council could have intervened in the ships arrival in Napier.
"Local Government doesn't have that power," said Wise, who otherwise supports a call for an inquiry just as she expects reviews will be held over many aspects of the Covid-19 crisis.
• Covid19.govt.nz: The Government's official Covid-19 advisory website