Doctors' surgeries cannot access medical records, test results or appointment systems due to the cyber attack on the NHS.
Barnby Gate Surgery, Newark, has told patients to attend as usual but stressed that many of their systems are down due to the attack, which began on Friday at around 2pm.
Sally Dixon, practice manager, said: "The issue is that we are not able to log on to the appointment system.
"So we cannot look at repeat prescriptions and cannot make any appointments - we don't know who's coming in this week.
"We are taking things day by day. We have not been given any timescales about when this might be fixed.
"Patients are welcome to pop in and we can do what we can do.
"If people are worried about anything then please do give us a call.
"The doctors are here as normal but it's really the acute stuff that we can deal with."
Following a warning of a pending attack, staff at Lombard Medical Centre, Newark, were able to note down patients' appointments.
Debbie Swain, practice director, said: "We don't think anybody is going to be at risk because of this.
"Our message to patients is: Please only come to us if you need urgent care today. If it's a routine call, please come back tomorrow."
On a statement posted on its website, Balderton Surgery said it had been "severely affected" by the cyber attack. No clinicians have access to patient notes.
The surgery's phone lines have also been affected, so patients have been advised to call the emergency mobile phone number of 07492 509716, for urgent queries only.
Southwell Medical Centre has experienced the same problems and has asked that only patients whose situation is urgent to contact them.
A statement from the Belvoir Health Group, which manages surgeries in Bingham, Cotgrave and Cropwell Bishop, said: "We are still unable to access our IT systems this morning. Please only contact the surgery if your enquiry is urgent.
"We are unable to book appointments, issue prescriptions, view test results and other such basic functions. Our phones are working as normal but our staff will only have access to very limited information with which to help you.
"If you have an appointment today please phone the surgery for an update. We are unable to access booked appointments.
"If you need an appointment urgently please call us and we will do our best to help you. If your enquiry is not urgent we ask that you please wait until the situation is resolved before calling."
Have you been affected by the disruption to services? Contact Sam Parker on 01636 688467 or email email@example.com