Victoria’s embattled ambulance service declared another “code red” overnight after buckling under high demand.

The emergency procedure was implemented about 2am Sunday and lasted 90 minutes, during which those in Metropolitan Melbourne were urged not to call for an ambulance unless they were in a serious condition.

Hospital and emergency staff had to operate at limited capacity, while restricted access to triple zero meant some calls were potentially unanswered.

Under the crisis protocol managers must to return to duty to manage hospital transfers, the rapid offloading of patients at hospital and lower the number of patients being referred to other services.

Additional staff were also recalled and non-emergency ambulances responded to some cases.

It comes amid fresh concerns about COVID-19 outbreaks

At least two other code reds have been declared in recent months.

Ambulance union secretary Danny Hill previously said the system was struggling.

“The system is busier than it has ever been and that’s not because of an increase in strokes, heart attacks or car accidents, it’s because of an increase in reliance on triple zero,” Mr Hill said.

“It means [paramedics] won’t be finishing their shifts on time or getting a meal break and will spend a large part of their shift ramped at the hospital because there’s so many patients they’re bringing in.”

Melbourne law firm Slater and Gordon is said to be considering filing a class action lawsuit against the state’s triple-zero authority, due to recent deaths linked to internal failures.

Thousands of Victorians could join the lawsuit against the Emergency Services Telecommunications Authority, following a series of fatal system errors that have led to at least 15 deaths and multiple injuries, including children, since 2014.

-AAP