Egyptian police have fired tear gas to disperse a rock-pelting crowd of residents defending their homes against bulldozers sent by the government to demolish the illegally-built dwellings.
The clashes left one person dead and 50 others injured.
The violence on the Nile island of el-Waraq on the southern fringes of Cairo is likely to stain a nationwide campaign launched this summer by Abdel-Fattah el-Sissi, Egypt's general-turned-president, to restore government control over state-owned land.
Mr el-Sissi has vowed in televised comments to show no lenience to anyone taking illegal advantage of state-owned property, saying the law would prevail regardless of how powerful or wealthy the offenders were.
Anyone using land that does not rightfully belong to them, he angrily said, is a "common thief".
Illegal use of state land is widespread in Egypt, as well as building on agrarian land in violation of the law.
Since Mr el-Sissi launched his campaign earlier in the summer, local media has been showing images of police and army troops demolishing buildings illegally built or operating without a licence, attempting to project an image of a government keen on protecting what is being billed as "people's property".
To el-Waraq's middle class and poor residents, however, the sight of bulldozers coming to demolish their homes may have been more than they could bear at a time when they, like most Egyptians, are struggling to cope with soaring prices for food and services, a result of ambitious reforms introduced by Mr el-Sissi's government to revive the country's battered economy.
"Get lost! Get lost!" the protesters shouted at the scores of policemen who descended on the island early on Sunday, backed by bulldozers, scores of riot policemen and led by senior police generals.
The protesters, mostly young males, succeeded in forcing the bulldozers to turn away, but clashes soon began.
The Health Ministry said a resident died and another 19 were wounded in the clashes. It did not say how the man, Sayed el-Tafshan, died, but a photo of his body posted on social media networks showed chest wounds compatible with birdshot.
The Interior Ministry, which controls the police, said its forces only used tear gas.
A ministry statement said a total of 31 people - policemen as well as contractors who arrived with them on the island - were injured in the clashes. The injured policemen included two generals.
Ten residents were arrested for their part in the violence, it added.
Video clips posted on social media networks showed hundreds of angry islanders, mostly young men, at the man's funeral, marching through farm fields while chanting "We will sacrifice the martyr with our soul and blood".
The statement said the residents attacked police with firearms, birdshot guns and rocks, and that police responded with tear gas. It said up to 700 building and land violations were recorded on the island. It acknowledged the death of one islander and that 19 others were injured.
In el-Waraq, a mostly agricultural island with shoddily built apartment blocks, residents maintain that their homes are legal, citing the government's supply of drinking water and electricity.
One of the Nile's largest islands in Egypt, it is home to nearly 200,000 people and is linked to the mainland by six ferries.
"How is my home illegal when you have for years provided me with water and electricity," said resident and civil servant Mahmoud Essawi. "It's our land and we are not leaving."