A Cathay Pacific Airbus bound for Hong Kong had to make an emergency dive to restore oxygen levels after a fault caused the cabin to depressurise, the airline said yesterday. The jet, carrying 232 passengers from Auckland, started to lose oxygen about four hours after take-off on Saturday and had to divert to Sydney. Engineers and aviation experts were investigating the 340-model Airbus yesterday to determine the cause of the incident. No one was injured. The depressurisation occurred about 288km north of Brisbane. Pilots had to override the computerised flight program to perform a manual dive from more than 31,000 feet to 8,000 feet in two minutes, according to a passenger who monitored his flight information screen. 'My ears were popping. Air masks were dropping all over . . . but the worst thing was most of them had no oxygen,' New Zealand businessman Tony Allen said. 'People were scared for their lives. I heard a passenger in the back become hysterical when we landed. 'A co-pilot told me that door seals had caused the problem, but the engines were fine . . . I think the masks just didn't work.' Cathay could not confirm the aircraft's altitudes last night, but said a rapid drop in height to less than 10,000 feet was a standard manoeuvre to restore cabin pressure and oxygen levels. 'It's a standard procedure that all our pilots are well-practised in,' a spokeswoman said. 'Safety levels for passengers are below 10,000 feet in terms of oxygen supply and dropping over two minutes for a plane is actually quite a long time.' She would not confirm whether the air masks had malfunctioned, adding that pilots could have manually switched off air supply after they found oxygen levels to be adequate. The 232 passengers eventually boarded another flight, CX100, and arrived in Hong Kong yesterday at 1.15pm. They were scheduled to arrive on flight CX108 at 8.30pm on Saturday.