Egyptian police fired tear gas on Sunday at garbage collectors who pelted them with rocks and bottles over fears they had come to seize their pigs as a precaution against a new flu virus.

At least 10 people were injured in the clashes in Manshiet Nasr, a shantytown on Cairo's outskirts where residents burnt trash barriers in the street to keep police at bay. Security sources said up to 15 people were detained.

Three police were also injured in clashes with pig farmers in another area of the capital.

Egypt, already hit hard by bird flu, ordered the slaughter of all Egypt's roughly 300,000 to 400,000 pigs on April 29 as a precaution against the H1N1 swine flu virus, a move the United Nations said was "a real mistake."

Egypt, which has not reported any H1N1 cases, fears another flu virus could spread quickly in a country where most of the roughly 80 million population live in the densely packed Nile Valley, many in crowded slums around Cairo.

One security source said police had gone to the Manshiet Nasr neighbourhood, a mix of concrete and brick apartment blocks and makeshift shanties, to seize pigs belonging to garbage collectors who make their living sorting trash.

But another security source said police were simply surrounding the neighbourhood to prevent residents from moving their animals outside the neighbourhood to hide them from officials seeking to enforce a cull.

"We serve the people and they come and cut off our livelihood. The pigs don't have any disease. The country is diseased. Take samples from the pigs and if they have disease, we would cull them," Manshiet Nasr resident Marzouk Badr Adli said after the clashes, complaining about the cull.

The new virus strain -- a mix of swine, avian and human viruses -- is being spread by people, not pigs. But culling swine, largely viewed as unclean in Muslim Egypt, could help quell any public panic in the most populous Arab country.

Pigs are mainly raised by the Christian minority, and government officials have complained that some farmers are trying to hide their pigs, making it harder for officials to carry out the cull.

The World Health Organisation has identified 787 H1N1 infections in 17 countries, including in Egypt's neighbour Israel, and said there were 19 confirmed deaths in Mexico.