The Highlands' largest hospital has been placed on "code black status" after reaching capacity amid increasing Covid cases.
NHS Highland said staffing and services at Inverness' Raigmore Hospital were under pressure due to large numbers of staff having to self-isolate.
The health board said its other hospitals and services were facing similar challenges with staffing.
All non-urgent elective surgery has been cancelled.
Outpatient activity - with the exception of cancer, urgent and some other activities - has also been cancelled.
NHS Highland said its area was seeing more than 100 cases on a daily basis. In June, it had more than 1,300 cases which is about a fifth of the health board's total number of cases since the start of the pandemic.
It said there were outbreaks in care homes, and on social media it has appealed to the public to follow advice on how prevent the spread of the virus with the message: "Highland Needs You".
NHS Highland patients were also experiencing long waits for treatment at Raigmore's emergency department.
It said pressure on its services had been increasing over the past week, and affected its sites in Highland and Argyll and Bute.
NHS Highland said: "The number of Covid-19 cases across our area has increased significantly.
"This is impacting on NHS Highland as some of these cases are now being admitted into our hospitals."
It added: "We are also seeing the impact on a large number of our staff, across a number of settings, who are having to self-isolate leading to gaps and pressures in our service. In addition to this we are also at the beginning of the summer school holidays and planned annual leave."
The health board said care and treatment of cancer and urgent cases would continue and it would also, where possible, carry on with orthopaedic and day case work.
Dr Boyd Peters, medical director for NHS Highland, said: "We are doing all we can to safeguard services but we have had to make the difficult decision to cancel non-urgent work which I know many will find upsetting and frustrating.
"We are very sorry that we have had to do this."