Ashcroft Surgery, on Newlands Way, Eccleshill, said its computer system and telephone lines are down.
It has left staff “unable to access medical records”, according to the voicemail message.
The GP practice apologised to those affected as it is unable to see patients until the issue has been resolved.
A spokesperson for the Bradford District and Craven Health and Care Partnership said: “There is an issue with the IT systems that service local GP practices across Bradford District and Craven.
“As a result, patients may have appointments delayed and may find it difficult to contact their GP practice over the telephone and online through practice websites. Please attend any booked appointments unless you are contacted.
“If anyone has any issues contacting their GP and needs medical help right now, please visit 111.nhs.uk or phone 111 and let them know you’re unable to reach your practice. Continue to only use 999 if it is a life-threatening emergency.
“The Health Informatics Service (THIS) is investigating the issue. This is not considered to be cyber related and patient data remains secure.”