Computer services are being restored to 80 NHS trusts in the North West of England and West Midlands following a massive IT failure on Sunday.
The crash meant staff could not check patients' appointments or access details of admissions and transfers.
About 40% of affected trusts are believed to have had service restored.
NHS Connecting for Health, which runs the health service's IT programme said services should be fully restored on Thursday morning.
Eight major hospitals and more than 70 primary care trusts in north-west England and the West Midlands were hit.
The failure means staff have to log patient movements manually, but no clinical information has been affected.
A spokesman for University Hospital, Birmingham, said it hoped to have its system back up by Tuesday afternoon.
Round the clock
The problem affects trusts in Birmingham and the Black Country, Cheshire and Merseyside, Cumbria and Lancashire, Greater Manchester, Shropshire and Staffordshire and the southern part of the West Midlands.
"The NHS cannot rely on a computer system that is only right most of the time"
Computer company CSC, which runs the system, said experts were working around the clock to resolve the situation.
A spokesman for NHS Connecting for Health, which oversees the multi-billion pound NHS IT service, said that no data had been lost, and that the incident was caused by "storage area network equipment failure".
The NHS Programme for IT aims to link more than 30,000 GPs to nearly 300 hospitals by 2014.
It is set to include an online booking system, a centralised medical records system for 50 million patients, e-prescriptions and fast computer network links between NHS bodies.
'Alarming'
A spokeswoman from the Department of Health said: "It is regrettable that the issue in the North West and West Midlands is causing inconvenience to patients.
"However, the affected NHS trusts have back-up systems to ensure they can continue with their day-to-day business.
"NHS Connecting for Health is working quickly with the supplier of the computer system to resolve this issue as quickly as possible."
Shadow health minister Stephen O'Brien said: "Despite the huge amounts of taxpayers' money which has been sprayed at the NHS IT system, it continues to be left wanting."
Liberal Democrat health spokesman Steve Webb said: "It is very alarming that trusts are reporting practical problems with a multi-billion pound IT system.
"The NHS cannot rely on a computer system that is only right most of the time."
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