As coronavirus cases spike in Korea, the NZ Defence Force is flying some personnel and their families based in the country home.

More staffers, now aboard the Navy's newest ship as it undergoes sea trials, will set sail for New Zealand when the testing finishes on Thursday, a NZ Defence Force (NZDF) spokeswoman said.

But the spokeswoman refused to say how exactly the NZDF was protecting the public or its staff from the risk of coronavirus infection from the evacuees.

"The NZDF is following current Ministry of Health guidelines for service members and civilian staff. No further details will be given at this stage," she said.

Those guidelines say people returning from mainland China, Iran, northern Italy or the Republic of Korea should self-isolate for 14 days from their date of departure.

On Wednesday, the spokeswoman said the NZDF decided the previous week to return some members of the Maritime Sustainment Capability project team and their families based in the Korean port city of Ulsan, in the south-east of the country.

Ulsan is just 70km from Daegu, the centre of the Korean coronavirus outbreak.

The number of confirmed cases in Korea has now passed 5000, the highest number outside China.

At least 28 people had died of the virus in Korea as of Tuesday, the country's Centers for Disease Control and Prevention said in statement.

Aotearoa, the largest ship the Royal New Zealand Navy has ever had in its fleet, was purpose-built in a shipyard in Ulsan and launched in April 2019.

It will replace the HMNZS Endeavour and operate as a fleet tanker, a supply ship and in support of maritime operations generally.

While some "non-operational" NZDF activities and travel had been affected, there were currently no plans to bring home any personnel on operational deployments due to COVID-19, the spokeswoman said.

"We continue to look at non-operational activities on a case by case basis."

NZDF personnel are currently deployed as far afield as Egypt, the Golan Heights and Iraq.

Six are deployed to the United Nations Command in the Republic of Korea (South Korea), including two officers in the  Demilitarised Zone, the buffer between South and North Korea.