Air New Zealand's booking and check-in system and Bank of New Zealand's online banking services were brought to their knees on Wednesday night by a further power failure at an IBM data centre. Air New Zealand was forced to switch to manually checking in passengers on several international flights when its computer system failed at about 9.30pm on Wednesday. At the same time the airline's online booking system was also unavailable for about an hour. Bank of New Zealand said its online banking service was down for about two hours, and the bank's other systems were affected by the outage to varying degrees for about four hours. BNZ Spokeswoman Erica Lloyd said customers were still able to do their banking through call centres. IBM spokeswoman Kate Woodruffe said its Newton datacentre, in Auckland suffered a brief power outage shortly after 9pm during routine maintenance. The centre's uninterrupted power supply (UPS) "took several seconds to activate". It took some time to bring the servers back online. A UPS is designed to smooth out brown-outs and spikes in the electricity supply and provide battery back-up in case of a power cut. Systems had been fully restored and IBM was "undertaking a thorough investigation into the root cause of the outage", Ms Woodruffe said. It is the second time that the data centre's back up power system has failed to work correctly. Air New Zealand's computer systems were crippled on the last day of last year's October school holidays, stranding more than 10,000 passengers around the country and delaying dozens of flights, after a power generator at the data centre failed due to a faulty oil pressure sensor. Air New Zealand chief executive Rob Fyfe at the time labelled the global computer giant's slow response to the crisis "amateur". BNZ's online services were also affected then. Air New Zealand announced in August that it was moving its primary data centre requirements to spread the risk of future failures. IBM is a secondary provider.