The Cornish tourist board has asked people not to visit unless they have pre-booked and are willing to test themselves extensively.
Chief executive of Visit Cornwall Malcolm Bell said visitors should aim to “treble their efforts as much as possible” with the hands, face, space guidance and try to remain outdoors.
Visitors have flocked to the area throughout the summer holidays which has seen a rise in infections.
Health agency data shows both Devon and Cornwall had 500 cases or more per 100,000 people in the seven days to August 18.
A week before, the figure was 300 or less per 100,000 people.
Mr Bell said: “We are asking people not to come unless they have booked ahead and request they take a lateral flow test before, during and after their stay so that people can be safe and help us to manage the current spike.”
On Monday, health officials said they were investigating 4,700 cases of coronavirus which are suspected to be linked to the Boardmasters festival which took place nearly two weeks ago in Newquay.
The cases are spread across the country but around 800 are living in Cornwall, a council official confirmed.
“There is concern and most local residents will be happier in a week or so, when the peak season is over and an older demographic visits as there are too many occurrences of overcrowding in honey pots,” Mr Bell said.
“We are asking visitors to look at visiting other parts of Cornwall. We have over 300 beaches and lovely parts that can cope with visitors.”
He added the vaccination programme in the county was in “full flow”. He asked people due to arrive to be patient with businesses who are short staffed and to book ahead with activities.
Mayor of Newquay Louis Gardner said “it’s a perfect storm” after speaking to businesses this week.
“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,” he added.
A spokesperson for Boardmasters said the festival used the NHS Covid Pass app as a condition of entry to the festival or urged people to show proof of a negative test before entering.
They added more than 450 people tested positive and left the festival early or did not go in.
“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,” they said.
“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.”