Around 200 patients with the virus are at the hospital and at Pilgrim Hospital in Boston during a time of staff shortages caused by covid infection and self-isolation.
The critical incident which is the highest alert level to be classified under, was declared last night due to ‘the large number of patients requiring admission.’
Patient visiting has been suspended in all but exceptional cases, Lincolnshire Live reported.
Nearly all face to face staff training remains cancelled, but vital core learning, study leave and annual leave will continue to be in place.
Mark Brassington, United Lincolnshire Hospitals NHS Trust deputy chief executive said: “We declared a critical incident last night, Monday, January 4 at Lincoln County Hospital due to the large number of patients requiring admission.
"We are sorry for the waits that our patients have faced yesterday and overnight.
"The incident is being managed internally with support from our partners and patients should continue to attend appointments unless contacted directly.
He added: “The number of inpatients who have been confirmed as having COVID-19 across our sites remains higher than in wave one and we remain extremely busy across our wards and intensive care units.
The current incident is ‘compounded by challenges with staffing due to a lack of availability of colleagues due to a number of factors’, according to the health boss.
Mr Brassington added: "We would like to thank all of our colleagues for all they are doing to support each other and for continuing to care for patients during these difficult times.
“The public can help by ensuring they follow government guidelines to reduce the spread of Covid-19 and by ensuring they use the most appropriate NHS service for their condition.”
This news comes after the NHS covid alert level was raised from four to five, meaning there is great strain on health services.
The highest level of hospital alert was previously declared at the same Lincoln County Hospital and also Pilgrim Hospital, Boston in November when the number of patients with Covid-19 at both hospitals rose from 56 to 175 in just a week.