An investigation has begun after an emergency control room in Norfolk was left without power and unable to receive any 999 calls.

Staff at the East of England Ambulance Service Trust (EEAST) emergency control room in Norwich were unable to take any calls or dispatch vehicles as a result of the fault, which happened yesterday morning.

A test of the ambulance service's back up generator at the Hellesdon office, in Hospital Lane, led to the power being off for around half an hour.

Officials from the NHS trust said that 999 calls were diverted to EEAST control rooms in Chelmsford and Bedford during the incident that happened at about 7am.

A spokesman for the ambulance service said they were 'actively investigating' the incident and whether any ambulances had been delayed because of the power failure.

'The trust carried out a routine generator test yesterday in Norwich, where we switch from mains power to back up generator power to test our contingency plans. During this test we experienced a failure which meant that for a period of about 30 minutes 999 calls were handled by our two other control rooms as part of our contingency arrangements whilst everything was restored,' the spokesman said.

The Hellesdon control room answers all the 999 ambulance calls from across Norfolk, Suffolk and Cambridgeshire and staff are responsible for dispatching rapid response vehicles and ambulances to patients.

The control room is also home to the Norfolk non-emergency 111 service.