Australian cattle are being killed with sledgehammers in Vietnamese abattoirs, according to a complaint lodged with the federal Agriculture Department by an animal rights group.

Animals Australia lodged the complaint with the department last week, after documenting the brutal practices in Vietnam last month. The organisation's communications director Lisa Chalk said the footage of the cattle being killed was "so shocking and distressing" that the organisation had decided not to publicly release it at this time.

Animals Australia has included this photograph, taken inside a Vietnamese abattoir last month, in its complaint to the Department of Agriculture. Credit:Animals Australia

Ms Chalk said Vietnam was currently the second largest export market for Australian cattle, with 178,000 animals exported there in 2014.

She said cattle and buffalo were traditionally slaughtered in Vietnam with repeated blows to the head with a sledgehammer.