The group arrived in Auckland on Monday from a southeast Asian country and were taken by minibus to their deep-sea fishing vessel in New Plymouth.
Roper said the company had not been advised by the Ministry of Health of plans for the vessel with all crew onboard to return to Port Taranaki.
From there, the crew was meant to be transferred to a managed isolation facility, Roper said, but allowing that transfer via the port would risk the health of workers and the community.
"Throughout the Covid-19 pandemic and our response to it, the health and safety of our staff, other port users and the Taranaki community has been our priority," Roper said.
As well as the safety aspect, Roper said the company had to consider staff resourcing and customers.
The port had a limited number of pilots and the pilot on duty for the vessel's return would likely need to self-isolate and be unavailable for work, he said.
"There is also no certainty about how long the fishing vessel would need to remain berthed without appropriate manning," Roper said.
"For those reasons we have decided that the vessel will not be returning to Port Taranaki."