Cumbria has suffered its "worst week" for Covid-19 infections with hospitals coming under "intense pressure", the council has said.
Cumbria County Council said 3,489 people tested positive in the week ending 8 January - a rise of 39%.
The north of the county saw a 63% jump in the number of hospital patients in a week, when it was announced outpatient services would be suspended.
Public health director Colin Cox said the situation was "extremely serious".
Latest figures also show that the 45-54 age group accounted for the greatest number of new cases, followed closely by the 25-34 age group.
Mr Cox said: "In the very latest provisional data there are some early signs that the rate of increase in new infections may be slowing, but the infection rate is still very high.
"Even if that trend continues, we can expect the very high numbers of people requiring hospital care, and increasing deaths, to continue for some weeks.
"This is putting our local NHS system under intense pressure.
"I cannot stress strongly enough how important it is that we all follow the lockdown rules."