Almost 5,000 coronavirus cases are suspected to be linked to a surf and music festival in Cornwall.

Health officials have launched an investigation after it emerged 4,700 people had tested positive for COVID-19 following Boardmasters near Newquay earlier this month.

Around 800 are thought to be living in Cornwall, but the cases are spread across the country, a council official said.

The sold-out event – which featured headlining acts Foals, Gorillaz and Jorja Smith – was held from 11-15 August.

According to the Boardmasters website, festival goers aged 11 and above were asked to demonstrate their COVID-19 status via the NHS app before being allowed to enter.

This required attendees to prove one of the following: they had been double vaccinated, with the second dose given at least a fortnight before the event; a negative lateral flow test taken within 24 hours of arriving at the festival gates; or natural immunity after a positive PCR test – taken at least 10 days earlier.

Camping ticket holders also had to take a second NHS lateral flow test during the event on Friday 13 August – then register their results on the NHS app.

Festival-goers were asked to bring their own lateral flow tests.

Face masks were “encouraged and welcomed for those who would prefer to wear them”, but not compulsory, the website said.

A Boardmasters spokesperson said its staff have worked closely with Cornwall Council’s public health team to implement risk management measures “above and beyond national guidelines” – including using COVID certification via the NHS app as a condition of entry.

“The system detected more than 450 people who would otherwise have been at risk of passing on the virus and as a result did not attend our Watergate Bay site or left the festival early,” the spokesperson explained.

“We are grateful to them and everyone else who took the extra steps this year.

“No event is able to eliminate risk entirely and the latest Test & Trace data includes reported infections among the 76,000 people who visited the festival or related activities at Fistral Beach, in Newquay and the wider area during the week of Boardmasters.

“We will continue to work with our public health partners to understand the extent to which attendance at the festival has contributed to the figures.

“We look forward to sharing our experience with our local authority partners and other large events so we can all continue to provide much needed economic benefit to our communities and entertainment to our loyal audiences.”

It comes as Cornwall and the Isles of Scilly recorded the second highest rate of coronavirus out of 312 areas in England, up from 383.5 per 100,000 to 717.4 – with 4,129 new cases in the week up to 19 August.

Sedgemoor in Somerset has the highest rate, with 892 new cases in the same period.

This equates to 722.6 per 100,000 people – up from 524.9 in the previous week up to 12 August.

Now business leaders are blaming a “perfect storm” of a huge influx of visitors and a lack of social distancing on the surge in cases in Cornwall.

Mayor of Newquay, Louis Gardner – who owns a deli in the town – said: “We’re seeing a spike in Cornwall because we’ve got the highest number of visitors we’ve ever had.

“Our accommodation is at 100% capacity, our hospitality venues are full, there’s no social distance in place, but I think those factors all added in all together are having an effect. It’s a perfect storm.”

Mr Gardner urged visitors to be respectful, adding: “Don’t come down here thinking that you’re on holiday and it’s not gonna affect you because it absolutely is.

“You’ve got a higher chance of getting Covid by coming here than you have by staying at home.”