An explosive fire at a Geelong oil refinery – which supplies half of Victoria’s fuel and 10% of Australia’s – has been extinguished, with the impact on petrol production and the extent of the damage still unknown.

The blaze at the Viva Energy facility in Corio – one of two refineries left in the country – broke out just after 11pm Wednesday, with Fire Rescue Victoria alerted to the blaze by multiple calls to triple zero reporting explosions and flames.

It continued to burn for 13 hours before FRV confirmed it had been extinguished. It was deemed under control shortly after 12pm on Thursday.

The federal energy minister, Chris Bowen, said the fire during a fuel crisis was clearly “not a good development” but said Viva was confident disruptions would be minimal.

“We don’t know exactly what the impact on petrol production will be,” Bowen said. “To be fair to everyone, we’re still assessing the damage.”

Bill Patterson, Viva Energy’s executive general manager of energy and infrastructure, said while the cause of the fire was still being investigated there was no indication it had occurred because of maintenance issues or an increase in production at the site.

He said the affected area was part of the refinery responsible for combining LPG into gasoline-type molecules, which were later used in fuel blending and specialty products.

“Obviously, we’ve still got to look into the full extent of the damage as we get better and better access to the scene, and that’s definitely very much work in progress,” Patterson said on Thursday afternoon.

“We’re still making petrol, diesel and jet fuel at pretty decent rates, so it hasn’t been a very large impact at this stage.”

FRV said the blaze “appears to have been caused by an equipment failure” and it would investigate alongside WorkSafe, Victoria police and Viva Energy.

“Firefighters remain on scene and we continue to monitor the situation and work with Viva and partner agencies to ensure the safe operation of the site,” FRV said.

No one was injured in the blaze but a watch-and-act alert urging residents to shelter indoors was issued at 1am, which was downgraded to an advice message on the VicEmergency website about 5.30am. It has subsequently said there was no longer a threat to the publicand residents were “able to resume normal activities”.

Authorities have stressed that hazardous materials teams have not detected any contaminants in air or water tests.

The source of ignition, and details about how much damage has been caused and what works will be needed to rectify it, will take place in coming days, FRV incident controller Anthony Pearce said.

“There is still a lot of flammable materials in the area that’s affected by fire, and we’re working with Viva to ensure that is isolated and there are no further ignitions,” said the FRV’s incident controller, Anthony Pearce. “The remainder of the plant is still functioning.”

Geelong’s mayor, Stretch Kontelj, described the blaze as “unprecedented” in scale.

The FRV deputy commissioner Michelle Cowling on Thursday morning said the fire’s cause appeared to be equipment failure – probably a leak or a valve malfunction within the refinery’s Mogas (motor gas) section.

“It was an equipment failure in the refinery, Viva is looking into that,” Cowling said. “There’ll be a thorough investigation into the failure [and] how this fire started.”

According to the Viva Energy website, the refinery can process about 120,000 barrels of oil each day. Last month the company said it was able to maintain supplies despite the war in Iran as it was not reliant on fuel from the Middle East.

Viva Energy’s chief executive, Scott Wyatt, said getting the site safe was the immediate priority, rather than any production factors.

“We’ll only start increasing production again once we’re confident we can do that safely,” he said.

Wyatt said the fire was in the petrol area of the plant, which “naturally” meant petrol products would be affected.

Speaking from Malaysia, Anthony Albanese said the fire was “very distressing” and there would be “consequences for fuel supply”.

“We’ll continue to work with the company to do what we can to make sure that anything that is offline is brought online as soon as possible,” the prime minister said.

Gero Farruggio, an analyst at Rystad Energy, said the government should move to stage-three fuel restrictions as a result of the blaze.

“Stage three should come in sooner rather than later, just to secure our supplies and manage demand and ensure we have enough reserves to get through this period,” Farruggio told ABC Radio Melbourne.

But the premier, Jacinta Allan, said such calls only caused “stress and uncertainty”. She said it was “too soon” to know the impact of the blaze.

“It will take some time to manage this site and then move to assessing the impact,” Allan said. “The advice remains … that our overall levels of supply coming into the country continue to support the level of activity that we need.”

The state’s energy minister, Lily D’Ambrosio, said there would be “no immediate impact on fuel supply”.

“[Viva] also have said that petrol or gasoline, of all of the fuel types that are under global pressure right now, is the most easiest fuel to be able to source,” D’Ambrosio said.

Ronnie Hayden, the state secretary of the Victorian branch of the Australian Workers’ Union, told ABC Radio Melbourne that between 50 and 100 workers had been on site when the fire broke out and that the evacuation “went to plan”.

“These guys have been highly trained in emergency response and emergency evacuation, and I think that’s the main reason why there were no fatalities.”

Hayden said the Viva refinery was a “70-year-old facility” that had always required regular maintenance.