Tasmanian authorities are investigating allegations of severe animal cruelty at an abattoir in the Derwent valley, north of Hobart.

The ABC obtained graphic vision an animal welfare group has said shows the prolonged and unlawful suffering of pigs, sheep and cows at the facility.

Tasmania's Department of Primary Industries said it was taking the allegations seriously and was investigating for breaches of the Animal Welfare Act.

The abattoir strongly denied the claims, saying its operation is lawful and will take legal action.

Animal Liberation said the vision was filmed over four days last month and came from an anonymous source.

Spokeswoman Emma Hurst accused the abattoir of crossing a line.

"This is grotesque cruelty that we're seeing here...and it's completely unacceptable," she said.

"The footage shows animals being beaten with pipes, kicked in the head ...there's clearly failed attempts to stun the animals."

Operator angered by 'break-in'

The operator of Gretna Quality Meats, Michael Munning, said he trusted his workers.

He admitted a rifle had been used but dismissed claims of cruelty.

Mr Munnings was happy to be interviewed and invited the ABC into the abattoir ... a small operation employing just three people.

He said he was angry and that the vision was illegally obtained while his operation acted lawfully.

"It's very frustrating that somebody's actually gone to the trouble of breaking into the property and actually putting up cameras," he said.

"It's a small country abattoir, small country town, it's just something that doesn't happen."

Rifle used not suitable: vet

The abattoir admits a rifle was used to shoot a pig. ( Animal Liberation )

Former meatworks supervisor and vet of 43 years, Dr Andrew Nicholson, said he had some concerns based on the vision.

"I'm not a firearms expert but obviously the rifle, as it was used that vision, was not suitable because from what I saw there were at least two shots taken...neither were effective," he said.

"That should be carried out as a single shot — the animal should drop immediately.

"Under the circumstances demonstrated in the vision ... that's not adequate.

"There was a lot of trouble restraining the animal effectively for the rifle to be used," he said.

Dr Nicholson said the facilities needed to be adequate to ensure animals were handled with minimal distress.

"In an abattoir situation there should be facilities that are adequate to move the animals from place to place, to be able to hold the animals on the facility and move them around with not having to use goads or steel bars," he said.

Vision shows nerve reaction post-death: operator

Michael Munnings says the captive bolt guns at his abattoir are regularly maintained. ( ABC News )

Also alleged is that the larger animals, which should have been knocked out, were alive and conscious for a prolonged period of time.

Dr Nicholson said in one instance on the vision, he could not say for sure that the stunning procedure had been effective.

He could see some signs of breathing, but he emphasised it was difficult to decipher.

"If you're not used to that type of thing it can be quite distressing," he said.

"The only comment I'd make on that is you couldn't make an effective judgement without being present at the time of stunning ... and neurologically examining that animal.

"The best-intentioned people can find it difficult if the facilities are not adequate and you can have the best facilities in the world, but if you haven't got skilled staff available on the day, problems can occur," he said.

Operator to complain to police

Mr Munnings insisted that the animals were already dead.

"A lot of the footage shows the nerve reaction from the animal and sometimes it can last up to two minutes, the nerves," he said.

"But the animals are already dead."

The meatworks said it would be reporting the break-ins to the police.

It is not clear how long the department's investigation will take.