The NHS has been hit with a massive computer outage, with 80 NHS Trusts in the North West and West Midlands unable to access their systems since 10am on Sunday.

Technical problems in a data centre in Maidstone are to blame, NHS Connecting for Health (CfH) has admitted.

The problem originated with a storage area network fault in a data centre operated by CSC Alliance. CSC operates patient administration, clinical records and other national programme systems for the North West and West Midlands under a £973m deal signed in December 2003.

"Technical issues following power system interruptions mean that data held on computers in the central data centre for the region cannot be accessed," said CfH and CSC in a statement. "The nature of the incident meant that service could not immediately be provided by the back-up systems, also provided by CSC Alliance. No data has been lost."

CSC and its subcontractor, Hitachi, are working to restore access to the system and CSC said some priority systems had begun to come back online. Seventy-two primary care trusts and eight acute hospital trusts have been affected. University Hospital in Birmingham is hoping to have access again by Tuesday afternoon.

The outage has affected controversial new systems for theatre management and appointment bookings, forcing staff to make provisional appointments using a paper-based backup system, which will have to be confirmed once the systems come back online, creating an administrative backlog. Access to computerised medical records hasn't been affected.

The multi-billion pound NHS Programme for IT, run by CfH, aims to link more than 30,000 GPs to nearly 300 hospitals by 2014. The programme includes an online booking system, centralised medical records and e-prescriptions.

Shadow health minister Stephen O'Brien and Liberal Democrat health spokesman Steve Webb both called the government to task for the continued glitches to the system, with Webb calling the incident "alarming." The British Medical Association called for an independent audit in order to ward off "complete disaster."