The footage, supplied by the Farm Transparency Project, was allegedly filmed at three abattoirs in early 2023 by activists who say they installed hidden cameras in the factories at Laverton in Melbourne's west and Benalla in Victoria's northeast.

It shows the animals being bundled into confined spaces and gasping after allegedly being exposed to high levels of carbon dioxide so they are unconscious before death, known as 'stunning'.

Under Australian law, pigs must be stunned before their death in a bid to ensure they do not feel pain.

The only legal forms of stunning are by carbon dioxide exposure or by knocking them out with an electrical current to their head.

Activist Chris Delforce took responsibility for the footage and said it was the most horrible thing he had ever seen.

"Labelling this as humane is grossly deceptive," Mr Delforce said.

Australian Pork said farmers used methods backed by peer-reviewed scientific research into animal welfare and it was seeking the full recording so it could review the footage.

"The entire Australian pork industry takes the welfare of our animals through their whole life very seriously," it said in a statement.

RSPCA chief executive Richard Mussell said the organisation has concerns about the use of carbon dioxide gas to stun pigs.

He said while the use of gas over electrical currents meant animals could be stunned in groups with less handling and stress, welfare issues remained including concerns they still felt pain and some pigs would not immediately become unconscious.

"With over 5.5 million pigs slaughtered in Australia each year, it's time for industry to act to improve the welfare of pigs at slaughter," Mr Mussell said.

A national animal welfare task group previously committed to developing new standards and guidelines for the treatment of pigs but it's unclear when that will be delivered.

The Transparency Project wants Victoria to conduct an inquiry into carbon dioxide stunning and for the process to be banned.

The Australian Meat Industry Council would not comment on the footage but said any concerns about the treatment of animals should be reported to authorities immediately.

"Illegally obtained footage of this nature is inherently biased, is not based on context as it relates to the complexity of livestock processing and only is ever released to the media to push an agenda," the organisation said in a statement.

"The trespass and covert filming of any livestock facility is inherently dangerous and poses significant biosecurity, animal, and human safety risks that (the council) cannot condone for any reason."

The Australian Greens used the release of the footage to ramp up calls for an independent office for animal welfare, and stronger laws with greater enforcement powers.

Victorian Agriculture Minister Gayle Tierney said the government supported any advancements that reduced a pig's suffering before slaughter and developing new national pig welfare standards were a priority.

Federal Agriculture Minister Murray Watt described the images as distressing and said the government was phasing out live sheep exports, developing a new animal welfare strategy and creating a new Inspector-General for Animal Welfare.

"I understand that the Victorian regulator is carefully reviewing the footage and is actively making further inquiries," Mr Watt said in a statement.

Australian Associated Press