Five positive coronavirus cases have been confirmed across Orkney as the head of the local health board warned the virus is “spreading rapidly” on the islands.

Authorities say the cluster is linked to a fishing vessel with an investigation now underway alongside contact tracing across NHS Highland, NHS Grampian and NHS Orkney.

Earlier on Thursday, NHS Orkney chief executive Michael Dickson said a number of people had developed symptoms and then travelled to their homes across Orkney and to mainland Scotland.

He said the cluster involves a minimum of nine people, some of whom have tested positive, with work ongoing to trace contacts.

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Louise Wilson, NHS Orkney director of public health, said: “Following their identification, the individuals have been asked to self-isolate and we are tracing all of their contacts, who will also be asked to self-isolate as a precaution.

“All of the positive cases have mild symptoms.

“To respect and maintain patient confidentiality we will not be releasing any further details at this time.

“A further update will be provided following the next incident management team (IMT).

“We are taking all necessary steps to contain this outbreak but it is vital people follow the FACTS guidance to limit the spread of the virus.”

Mr Dickson previously told BBC Radio Orkney the latest cases involve a group of people who worked together with early signs indicating a possible link to Aberdeen.

At the Scottish Government’s daily coronavirus briefing earlier on Thursday, Nicola Sturgeon said there were three new cases in NHS Orkney in the past 24 hours with an incident management team due to meet later that day.

NHS Orkney last reported a positive case on June 15, when there had been a total of nine cases since the start of the pandemic.

However on Saturday the health board said Orkney testers had picked up a positive case registered to a mainland address.

The First Minister said: “While Orkney had a number of cases at the beginning of the pandemic, it has had very few since, so I would urge everyone on the islands to guard against complacency.

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“If you have what might be symptoms of coronavirus please isolate immediately and make immediate arrangements to be tested.”

Orkney MSP Liam McArthur also said: “This spike in new cases is deeply worrying.

“It is also a timely reminder that this virus remains a real threat and that we all have a responsibility to act with the utmost care to keep ourselves and our community safe.

“I will also be speaking to the Health Secretary later today to establish what further action is being considered to contain this outbreak and minimise the risk to the public.”