A crew member on a vessel that's docked at Port of Tauranga is suspected to previously have been infected with Covid-19.
The Ministry of Health is investigating the case on the IVS Merlion after the crew member returned a weak positive test result, with a high CT value, which indicates an old infection.
The vessel arrived into New Zealand waters on 15 October after departing Indonesia on 24 September.
The ministry said it was most likely that the person had been infected some time ago but was no longer infectious. They are now isolated as a precaution and have had a repeat Covid-19 test as well as a blood test to confirm whether their case is a historic one.
All the other crew members have tested negative and have been on board the vessel for three weeks, the ministry said.
The crew have also not come ashore, so there was very low risk of transmission, the ministry said.
All crew members are being treated as close contacts and none are allowed to leave the vessel until the investigation is complete.
The health staff and other port staff, who had minimal contact with the crew, have all been informed.