The Australian navy’s largest ship docked in Tonga on Wednesday and was allowed to unload humanitarian supplies to the South Pacific nation despite crew members being infected with Covid-19, officials said.

Nearly two dozen sailors aboard HMAS Adelaide were reportedly infected on Tuesday, raising fears that the mercy mission could bring coronavirus to the small archipelago devastated by an undersea volcanic eruption and a tsunami on January 15.

Since the pandemic began, Tonga has reported just a single case of Covid-19 and has avoided any outbreaks.

It is one of the few countries in the world currently completely virus-free. About 61% of Tongans are fully vaccinated, according to Our World in Data.

The 27,500 metric ton ship had completed the 2,050-mile (3,300km) voyage from Brisbane and would deliver supplies without contact with the local population to avoid infections, the Australian government said in a statement.

“We appreciate the decision of the government of Tonga to enable HMAS Adelaide to dock and offload the humanitarian and medical supplies, and the high priority it has placed on Covid safety throughout the recovery process,” the statement said.

“The ship is undertaking an entirely contactless delivery of humanitarian assistance and disaster relief supplies.”

With restoration of the drinking water supply a major priority, the ship brings a desalination plant. It is also carrying helicopters and engineering equipment.

Australia said it was widening its disaster support to include restoration of power and communications.

Tonga usually requires visitors to quarantine for three weeks on arrival and the tough pandemic measures complicate the international disaster response. All international aid is to be delivered without local contact.

Tongan authorities have been wary that accepting international aid could usher in a bigger disaster than the huge eruption of the volcano. The tsunami has claimed three lives.

The ship is the second aid mission from Australia in which at least one crew member tested positive. A C-17 Globemaster military transport plane was earlier turned around mid-flight after a person aboard was diagnosed with coronavirus.