Fernando Meirelles did boys with guns in "City of God" and murderous corporations in "The Constant Gardener." With "Blindness," the opening night entry at the Cannes Film Festival, the Brazilian director exposes the world's ultimate savages: your friends and neighbors.

A terrifying fable about how low people might go to stay alive when a plague of blindness turns them into helpless internees, "Blindness" presents an unnerving reflection of real tragedy and bureaucratic heartlessness, from Hurricane Katrina to global food shortages to the cyclone in Myanmar, where the military government has severely restricted relief efforts.

"There are different kinds of blindness. There's 2 billion people that are starving in the world," Meirelles said in an interview Thursday, a day after the film's Cannes premiere. "This is happening. It doesn't need a catastrophe. It's happening, and because there isn't an event like Katrina, we don't see."

Opening in U.S. theaters Sept. 19, "Blindness" is adapted from the novel by Portuguese author Jose Saramago, winner of the Nobel Prize for literature.

The film chronicles the panic, disorder and barbarity that erupts after a contagion spreads "white blindness" throughout an unspecified city, with people's vision replaced by a milky cloud.

Victims are crammed into decrepit, filthy wards and left on their own, with no medical care. Scant food is provided, and trigger-happy soldiers gun down anyone they think might make a break for freedom, though all the afflicted can do is stumble about aimlessly.

The inmates include an eye doctor (Mark Ruffalo) and his wife (Julianne Moore), who inexplicably retains her sight but feigns blindness so she can accompany her husband into detention. Among their roommates are an old man (Danny Glover), a prostitute (Alice Braga), a thief (Don McKellar) and a married couple (Yusuke Iseya and Yoshino Kimura).

While that group tries to maintain a degree of order, their neighbors in another ward declare themselves "Lord of the Flies"-style rulers, led by a man (Gael Garcia Bernal) with a gun and a willingness to let bullets fly blindly. His thugs take over the food supply and force the others to pay with jewelry, and later, with their women.

"The other day, I heard somebody say, `It's inhuman. It's not human.' No, it is. The movie, it is about human beings, and how in a way, we're animals," Braga said. "If you're put in a situation, that's what would happen."

The action sinks to its most brutal in a gang-rape scene, which precipitates violent retribution and an unexpected escape for some victims, who emerge into a city overrun by staggering, starving survivors, the blind literally leading the blind to scavenge for food.

Could so many people descend so completely into bestiality?

"Look at what happens in war, and how whole towns are raped," Moore said. "We have this idea that we've got it together, but you see what happens when there is a natural disaster. Things crumble. Things literally crumble. So the sense that, oh, we have secured this, we have taken care of this, we know how to do this. In fact, we're just a step away from chaos."

"We've seen food riots in Egypt, food riots in Sudan, food riots in Somalia, food riots in Haiti. Is that a test to see where we're going?" Glover said. "Do we have the political will worldwide to come to grips with that?"

Meirelles said the depravity in the story could go even lower.

"I think the next step would be cannibalism. Rape? How can you go lower? There's no food, so it could turn to cannibalism."

The film also incorporates wickedly dark humor, including a zinger that could be interpreted as a jab at President Bush and U.S. militarism after the Sept. 11 attacks.

"How lucky we are to have a leader with vision," one of Moore's charges remarks as she leads them through the horror of a city that has fallen apart.

"It has something to do, yeah, with the Bush administration," Meirelles said.

Amid the bedlam, glimmers of hope appear as the main characters forge a clan and reclaim a piece of their humanity.

"Toward the end of `Blindness,' they're reaching that point where they're redefining family and redefining civilization," said co-star McKellar, who also wrote the screenplay. "You give them time, and they would deal with it. If they were to remain blind, they would be all right."