Health authorities in Orkney say they are dealing with nine suspected cases of Covid-19.
They said they were examining potential links with cases on the islands and an outbreak in Aberdeen in which 177 cases have so far been confirmed.
NHS Orkney said those suspected of having the virus had all worked together.
It comes after the health board issued a warning that coronavirus was spreading “rapidly” across the islands.
A public health team is working to trace the close contacts of those involved.
The health board’s chief executive, Michael Dickson, told BBC Radio Orkney: “The biggest concern is that we’re talking a minimum of nine people, a number of which have already tested positive.
“The other factor is how distributed the are across Orkney and spreading across into the mainland as well. So it’s not only a case of having this number of people who may be symptomatic and some of which have tested positive, but it’s the distribution of them.”
Mr Dickson confirmed that the group of nine had all worked together and had been in “close contact”.
NHS Orkney has not officially confirmed a new case of the virus since 15 June, but Mr Dickson said the latest positive cases had been attributed to mainland health boards because of where the patients lived.
“We announced on Saturday that there had been a test positive case tested through the Orkney system - but that was registered to a mainland address,” Mr Dickson said.
“This is a separate cluster. The early signs are it may have a link back to Aberdeen.”
NHS Orkney said it was taking the cluster “extremely seriously” and working with mainland health boards, port authorities and ferry operators to try to limit the outbreak.
The health board urged anyone in Orkney who was showing symptoms to self-isolate immediately and seek a test.