Survivors of Tuesday’s earthquake extend their arms as U.S. troops with the 82nd Airborne Division distribute water Sunday in Port-au-Prince, Haiti. The troops gave out more than 9,000 bottles of water and 2,000 meals Sunday.

Port-au-Prince, Haiti ? Prayers of thanksgiving and cries for help rose from Haiti’s huddled homeless Sunday, the sixth day of an epic humanitarian crisis that was straining the world’s ability to respond and igniting flare-ups of violence amid the rubble of Port-au-Prince.

Haitian police struggled to scatter hundreds of stone-throwing looters in the city’s Vieux Marche, or Old Market. Elsewhere downtown, amid the smoke from bonfires burning uncollected bodies, gunfire rang out and bands of machete-wielding young men roamed the streets, faces hidden by bandanas.

A leading aid group complained of skewed priorities and a supply bottleneck at the U.S.-controlled airport. The general in charge said the U.S. military was “working aggressively” to speed up deliveries.

Beside the ruins of the Port-Au-Prince cathedral, where the sun streamed through the shattered stained glass, the priest told his flock at their first Sunday Mass since Tuesday’s earthquake, “We are in the hands of God now.”

But anger mounted hourly that other helping hands were slow in getting food and water to millions in need.

“The government is a joke. The U.N. is a joke,” Jacqueline Thermiti, 71, said as she lay in the dust with dozens of dying elderly outside their destroyed nursing home. “We’re a kilometer (half a mile) from the airport and we’re going to die of hunger.” Hours later, a frail resident of the home perished in the afternoon heat.

Water was delivered to more people around the capital, where an estimated 300,000 displaced were living outdoors. But food and medicine were still scarce.

The crippled city choked on the stench of death and shook with yet another aftershock Sunday. On the streets, people were still dying, people were on their knees praying for help, pregnant women were giving birth on the pavement, and the injured were showing up in wheelbarrows and on people’s backs at hurriedly erected field hospitals. Authorities warned that looting and violence could spread.

At the Vieux Marche, police tried to disperse looters by driving trucks through the crowds, as hundreds scrambled over partly destroyed shops grabbing anything they could. As he ran from the scene with a big box of tampons, Love Zedouni shouted: “I’ve got no idea what this is, but I’m sure you can sell it.”

Police used tear gas to scatter looters at street markets near the collapsed presidential palace. At the Cite Soleil slum, moments after police drove by, a reporter spotted a gunman stealing a bag of rice from a motorcycle rider.

“This is one of the most serious crises in decades,” U.N. Secretary-General Ban Ki-moon said as he flew into the Haitian capital. “The damage, destruction and loss of life are just overwhelming.”

A reliable death toll may be weeks away, but the Pan American Health Organization estimates 50,000 to 100,000 died in the 7.0-magnitude tremor, and Haitian officials believe the number is higher.

Celebrating Mass outside the once-proud pink-and-white cathedral, now a shell of rubble where a rotting body lay in the entrance, the Rev. Eric Toussaint preached of thanksgiving to a small congregation of old women and other haggard survivors assembled under the open sky.

“Why give thanks to God? Because we are here,” Toussaint said. “What happened is the will of God. We are in the hands of God now.”

Mondesir Raymone, a 27-year-old single mother of two, was grateful. “We have survived by the grace of God,” she said.

But others were angry.

“It’s a catastrophe and it is God who has put this upon us,” said Jean-Andre Noel, 39, a computer technician. “Those who live in Haiti need everything. We need food, we need drink, we need medicine. We need help.”

Were his parishioners being helped? Toussaint was asked. “Not yet,” he replied.

The U.N. World Food Program was “pretty well on target to reach more than 60,000 people today,” up from 40,000 the previous day, WFP spokesman David Orr said. But U.N. officials said they must raise that to 2 million within a month.