Cornwall's coronavirus infection rate is the highest its been since the start of the pandemic and the county is in a "serious situation", according to its Director of Public Health.
The latest official figures show the number of positive cases per 100,000 people is 320.
Rachel Wigglesworth, Cornwall's Director of Public Health, issued the stark warning to the county's residents during a media briefing on Wednesday (6 January).
She said: "This is a serious case for Cornwall, we've seen more than two thirds of the total case numbers for Cornwall just in the past two months.
"We've increased from a rate of 18 to over 300 per 100,000 - that is a rapid increase. It's a more rapid increase certainly than anywhere else in the South West but also nationally, so this is a serious situation for Cornwall."
She also said the virus "is very nearly out of control in Cornwall" and the message to stay at home "is really simple".
Before Boris Johnson introduced a third lockdown for England, Cornwall and the Isles of Scilly was the only place in England to remain in Tier 1.
While there have been no new cases on the Isles of Scilly since September last year, cases in Cornwall have seen a "dramatic surge" according to the local council.
In a briefing on Wednesday (6 January), Rachel Wigglesworth said: "People need to take care, even within their households. Stay at home, but if anyone has symptoms please get a test and within the household keep your distance and prevent onward spread.
"We’re seeing household transmission very quick and also into the workplace so please take precautions and help reduce the numbers”
Cllr Julian German, leader of Cornwall Council, called for tougher restrictions before the third lockdown announcement was made.
He said: "This action should have been taken as soon as the surge in case numbers became evident. My hope now is that these steps will prove enough to make a real difference and reduce the spread of the virus."
Cllr German also said people must "take lockdown seriously" amidst a backdrop of growing pressure on local health care services.