Patients with planned procedures and operations at Royal Preston Hospital have been told they must wait a fourth day as delays continue.

Lancashire Teaching Hospitals NHS Trust said the cyber attack has affected their IT systems and the weekend cancellation of procedures continues into Monday.

Outpatient clinics are going ahead as planned but the Trust is warning there may be delays.

During Friday lunchtime a cyber attack saw a virus called ransomware affect the NHS’ computer system, it locked up computer screens demanding payment for them to be unlocked.

Read more: Preston GP describes what happened during ransomware shutdown

A statement released by Lancashire Teaching Hospitals – whose hospitals include Preston and Chorley – said: “The international cyber attack has affected the IT systems at Lancashire Teaching Hospitals NHS Foundation Trust.

“We are working round the clock to resolve this issue and minimise impact on our services.

“The majority of planned procedures and operations scheduled for Monday 15 May are postponed.

“Please do not come to hospital as your procedure won’t be going ahead, unless we have been in touch with you and advised you otherwise, or you are a chemotherapy, radiotherapy or dialysis patient. Chemotherapy, radiotherapy and dialysis treatment will go ahead as planned.

“Outpatient clinics will go ahead as planned on Monday, but there will be delays and patients whose appointment involves blood tests may need an additional follow up appointment.

“We apologise to every patient whose treatment has been affected.

“We will review the situation on Monday and confirm as soon as possible if any services will be disrupted on Tuesday.”

The Trust says its switchboard is experiencing high volumes of calls, so patients are advised to check the Trust’s website or follow them on Twitter.