A northern Sydney abattoir has been forced to close after footage emerged showing animals being beaten before their slaughter.

Late on Thursday the New South Wales Food Authority suddenly closed down the Hawkesbury Valley Abattoir after viewing video footage which it says reveals "acts of gross animal mistreatment".

The footage, taken secretly inside the abattoir, has been given exclusively to Lateline.

The NSW Food Authority is promising a full investigation of slaughter practices during the shutdown.

This morning, the NSW Department of Primary Industries said the abattoir was inspected four times last year.

Shot undercover over six days at the abattoir, the footage shows pigs being dragged onto the sticking table and being belted with what looks like an iron bar.

The pigs should be rendered unconscious by a stunner before their throats are cut, but the footage shows that it has not been done properly in some incidences.

It shows the slaughterman reaching for what looks like an iron bar.

On one occasion a pig's head was pummelled seven times. A minute later the same worker beat another pig over the head 13 times.

Animal Liberation's Emma Hurst says the footage shows "grotesque cruelty".

"It's absolutely hideous. Last year we saw footage from the live exports of the cattle live exports in Indonesia and some of the most horrific scenes that we saw in that footage was of cattle being slaughtered while fully consciousness and here in Australia at this abattoir we are seeing the same thing happen," she said.

Ms Hurst is calling for CCTV cameras to be installed inside abattoirs to help prevent animal abuse.

She says a regulator should assess footage periodically to ensure abuses do not happen.

Sorry, this video has expired Peter Day from the NSW Food Authority talks to ABC News Breakfast

Vet Dr Mark Simpson has compiled a report on the footage, which has also been handed to NSW Police.

He says he believes the footage shows more than 100 breaches of the Prevention of Cruelty to Animals Act.

He says the vision also shows that sheep are not being stunned properly.

"From the time they have their throats slit there shouldn't be any raising of the head, there shouldn't be any voluntary movement," he said.

Dr Simpson says the footage shows one of the animals trying to move its head around while it is bleeding out.

"So it will be losing consciousness but it can still sense what is going on around it," he said.

The footage also shows electric cattle prods being used to what Dr Simpson calls an excessive degree in another part of the abattoir.

"The internationally accepted standard is that less than 5 per cent of the animals that go through need to have a rod applied," he said.

"There is a piece of this footage where the whole footage, it wasn't selected, where 85 animals had the prod applied in excess of 100 times."

Earlier, one of the directors of the Hawkesbury Valley Abattoir, Glenn Langley, said he wanted 48 hours so he could take the footage to the regulatory authority and let them examine it.

In a statement the authority said the footage allegedly shows breaches of the Food Regulation 2010 and Prevention of Cruelty to Animals Act 1979.

"Australian standards under the Food Regulation 2010 require that 'animals are slaughtered in a way that prevents unnecessary injury, pain and suffering to them and causes them the least practical disturbance'," the statement said.

"A full investigation of slaughter practices at the site is now underway, which involves the RSPCA."

The owners of the abattoir say they will not make any comment until the investigation is complete.