Burgers containing 30 percent horsemeat have been found in supermarkets in the UK and Ireland.
An analysis of meat at three processing plants found 10 out of 27 beef products contained horse DNA.
The products were stocked in supermarkets including Tesco, Iceland Foods, Dunnes Stores, Lidl and Aldi − one Tesco burger was found to be 29 percent horsemeat.
The samples also showed 23 beef products and 21 frozen beef meals, including cottage pie and lasagne, contained pig DNA.
The products have been withdrawn from shelves.
Ireland's food safety authority chief executive Alan Reilly told the BBC that people who had consumed the horsemeat were not at risk, but said there was "no clear explanation" for its presence in beef products.
"In Ireland, it is not in our culture to eat horsemeat and therefore we do not expect to find it in a burger," Reilly said.
"Likewise, for some religious groups or people who abstain from eating pig meat, the presence of traces of pig DNA is unacceptable."
Tesco's group technical director Tim Smith issued a statement on the company's website confirming two of its products that had been found to contain horsemeat had been withdrawn from sale.
"We are working with the authorities in Ireland and the UK, and with the supplier concerned, to urgently understand how this has happened and how to ensure it does not happen again," Smith said.
"The relevant authorities have said that these findings pose no risk to public health. We understand that many of our customers will be concerned by this news, and we apologise sincerely for any distress."
Silvercrest Foods, one of the three processing plants involved, said it had never purchased horsemeat and would also launch an investigation into its suppliers.
There are currently two horse abattoirs in Australia — Peterborough in South Australia and Caboolture in Queensland — that export around 2000 tonnes of horsemeat to Eastern Europe and Asia every year according to the Australian Bureau of Statistics.
Western Australian butcher Vince Garreffa has also been selling it direct to the public since 2010 under a state licence.
A spokesperson from Aldi's told ninemsn that the horsemeat would not be found in products at their Australian stores.
"Aldi Australia’s beef burgers are not the same as Aldi UK’s beef burgers as they are sourced from different suppliers, use different recipes and are also made from 100% per cent Australian fresh beef," a spokesperson said.
Author: Laura Wakely
Approving editor: Rory Kinsella.