Almost two dozen sailors on an Australian military ship delivering aid to Tonga have tested positive for Covid-19, officials said.

Australian defence minister Peter Dutton said his government was working with Tongan authorities to keep the ship at sea and make sure there is no threat to Tonga’s 105,000 residents.

Tongan authorities have been wary that accepting international aid could usher in a bigger disaster than the huge eruption of an undersea volcano 10 days ago. The eruption triggered a tsunami that destroyed dozens of homes, and volcanic ash has tainted drinking water.

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.

Australian officials said 23 crew members were infected on the HMAS Adelaide, which left Brisbane on Friday.

“They need the aid desperately, but they don’t want the risk of Covid,” Mr Dutton told Sky News.

“We will work through all of that as quickly as we can.”

It is the second aid shipment 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 somebody was diagnosed.

Meanwhile, a cable company official said Tonga’s main island could have its internet service restored within two weeks, although it may take much longer to repair the connection to the smaller islands.

The single undersea fibre-optic cable which connects the Pacific nation to the outside world was severed after the eruption and tsunami.

That left most people unable to connect with loved ones abroad. For days, people could not get through on their phones, by email, or through social media.

Since then, Tonga’s Digicel has been able to restore international call services to some areas by using satellite connections. Some people have been able to send emails or get limited internet connectivity.

Samieula Fonua, who chairs the board at Tonga Cable Ltd, the state-owned company which owns the fibre-optic cable, said a repair ship had left from Papua New Guinea and was due to stop over in Samoa by Monday to pick up supplies. It should then arrive in Tonga by February 1.

He said that all going well, the crew should be able to repair the cable by February 8, restoring the internet to about 80% of Tonga’s customers.

A second, domestic fibre-optic cable that connects Tonga’s smaller islands to the main island could prove much more difficult to repair.

Mr Fonua said that cable runs near the undersea volcano which erupted and may have been severely damaged and might need extensive repairs or even a replacement.