Almost a third of junior doctors in Victoria's public hospitals have considered quitting during the pandemic, a survey has found.

According to the snapshot by the Victorian branch of the AMA, 32 per cent of 1100 doctors surveyed have considered walking away from their job, with overwork and COVID-19 affecting their mental and physical health.

Of those who were thinking of resigning, 16 per cent considered quitting often or very often, and another 16 per cent thought about it sometimes.

The coordinator of doctors in training at AMA Victoria Dr Gavin Wayne said morale is at an all-time low, and the hospital system is at "breaking point".

"For decades health administrators and various governments have relied on our doctors who are regularly working up to 25 hours a week overtime, most of it unpaid," he said.

"It's clear exploitation, embedded into our health system."

Dr Wayne said the systemic exploitation of junior doctors will be the only thing keeping hospitals going in 2022, when health services will be trying to catch up with a backlog of treatments delayed by COVID.

It comes as more class actions were filed this week against three of the state's biggest health services.

The cases, filed in the Federal Court against Northern Health, Alfred Health and St Vincent's Hospital, allege systemic wage theft from junior doctors.

Class actions have also been filed against Peninsula Health, Monash Health and Latrobe Regional Hospital, Western Health, Eastern Health and the Royal Women's Hospital earlier this year.

More than 1400 junior doctors have registered to participate in the class actions so far, claiming repayment for unpaid overtime, and alleged breaches of the Fair Work Act.

The Victorian health department has been contacted for comment.