Only one of the six hospitals met the performance standard for accepting ambulance cases in the period, the figures show.
The opposition released figures on Sunday obtained under Freedom of Information which it said revealed critical bed shortages and overflowing emergency departments.
The Victorian government dismissed the figures for the July-September period of 2009 as scaremongering.
Opposition health spokesman David Davis criticised the government for not having released the figures itself and for fudging the true extent of the problem by not counting so-called alert system 'diversions' of ambulances as bypasses.
Ambulance diversions occur when ambulances are turned away because an emergency department is full or unable to take more patients - either in official bypasses or under Hospital Early Warning Status (HEWS), an alert system that notifies ambulances that the emergency department is diverting cases.
Bypasses occurred most frequently at the Royal Melbourne and Western Hospital at Footscray, where ambulances were diverted in about nine per cent of cases, triple the government-set benchmark of three per cent.
The figures were between four and six per cent at the Sunshine, Eastern (Box Hill) and Maroondah hospitals, while the Angliss Hospital (Ferntree Gully) was under the benchmark (0.92 per cent).
The patient speeding towards the hospital is diverted to a different and more distant hospital, and their health is potentially compromised by those diversions, Mr Davis told reporters on Sunday.
John Brumby and his government promised more than 10 years ago to fix our health system.
John Brumby has closed hospital beds around Victoria... the failure to meet those benchmarks is a shocking indictment on John Brumby after 10 years of government, and this failure to provide proper services and its impact on patients means lives potentially are at risk.
One thing Mr Rudd could demand out of John Brumby is that the true number of hospital diversions be reported to the public.
However, Victoria's hospital system actually performs well despite a low number of beds, according to the Australian Medical Association.