Police fired shots in the air and used tear gas against pig owners who stoned them on Sunday to prevent government workers from slaughtering the animals as a precaution against swine flu in a slum district of Cairo, an Egyptian security official said.

A youth ducks during clashes between protesting pig farmers and Egyptian riot police in the neighbourhood of Manishyet Nasr on the outskirts of Cairo. (Nasser Nouri/Associated Press)

Twelve people were injured in Manshiyet Nasr, where impoverished garbage collectors live and raise pigs who feed off the refuse.

The security official, who spoke on condition of anonymity, said police were escorting government workers who came to haul the pigs away.

Egypt has ordered the slaughter of all the country's 300,000 pigs even though no cases of swine flu, or influenza A (H1N1), have been reported in the country.

The World Health Organization said a cull is unnecessary because the virus is being spread through humans.

"There is no clear indication that the current human cases with swine influenza infection are related to recent or ongoing influenza-like disease events in pigs," the UN agency said on its website.