PORT-AU-PRINCE, Haiti -- About 50 Haitian orphans arrived Tuesday at a Pittsburgh, Pennsylvania, airport and will be taken to Children's Hospital of Pittsburgh, where adoptive parents are expected to greet them.

The first children to leave the plane were infants wrapped in blankets.

The children were accompanied on the flight by Pennsylvania Gov. Edward Rendell, several doctors and a few members of Congress. These are children whose adoption cases were at the end of the bureaucratic process before the 7.0-magnitude earthquake struck Haiti last Tuesday.

Allegheny County spokesman Kevin Evanto told CNN that the children will be placed in foster homes until details of their adoptions are finalized.

In Florida, where evacuees have been ferried in since Saturday, more flights from Haiti were scheduled for Tuesday. Officials at Orlando Sanford International Airport expect arrivals for the next two weeks.

Meanwhile, frustrations have mounted in the Haitian capital, Port-au-Prince, even as rescue efforts have gained steam.

"We don't have anything to eat. ... We don't even have some water to drink," one woman told CNN.

A 5.8-magnitude earthquake struck off the coast of the Cayman Islands Tuesday, the U.S. Geological Survey reported. The Caymans are about 600 miles (1,000 kilometers) west of Port-au-Prince.

Hundreds of Haitians broke into a damaged store in downtown Port-au-Prince on Monday, stripping it clean and then moving on to another store a half-block away.

That seems to be an overwhelming challenge for the Haitian National Police, a force of about 9,000 now.

National Police Chief Mario Andresol told CNN on Monday that the department has been severely affected by the earthquake, with thousands of officers injured, killed or unaccounted for. The Port-au-Prince force of 4,000 has dropped to about 1,500, he said.

Complicating matters, the quake collapsed the overcrowded 95-year-old National Penitentiary, and its 4,000 inmates escaped.

"We have double work," Andresol said, adding that the police department is bringing in troops from other parts of the country. "There are not enough, so we are trying."

Despite the challenges, "overall, people are very calm," U.S. Ambassador to Haiti Kenneth Merten told CNN.

Haitian police and U.N. and U.S. forces are ready to provide security as needed, he said.

The U.S. military considers the security situation stable, Rear Adm. Mike Rogers, director of intelligence for the Joint Chiefs of Staff, told reporters Monday.

Nothing suggests widespread disorder and panic, he said, describing well-publicized incidents of unrest as "isolated events."

The country's roads and the capital's airport were so congested that the supply lines of goods into Haiti were clogged, leaving thousands of survivors to scrounge for food and emergency aid.

A U.S. Air Force C-17 circumvented airport congestion by dropping 55,000 pounds -- about 40 pallets -- of bottled water and food into Haiti on Monday, the first U.S. airdrop of supplies.

But the congestion and distribution problems showed signs of easing Monday, with 180 flights passing through the airport, said Gen. P.K. Keen, who is leading U.S. forces in Haiti.

During the previous day, more than 233,000 bottles of water and 140,000 meals were distributed, not enough for the 3.5 million people affected by the quake, he said.

He predicted that the quake-damaged port would open "in some capacity" by week's end.

And the dearth of hospital facilities also should ease soon, he said. Argentina, Israel, Portugal, Russia and Turkey have sent or are sending hospitals, he said.

The USNS Comfort, a hospital ship, was en route, he added.

A lack of resources, communication difficulties and crippled infrastructure continued to slow medical efforts, officials with the Pan American Health Organization told reporters Monday.

Médecins Sans Frontières -- also known as Doctors Without Borders -- said flights carrying medical equipment were being diverted to the Dominican Republic. Oxfam warned of looming fuel shortages. And a volunteer at a hospital in northern Haiti said he had open beds, but no way to get patients there from Port-au-Prince.

But doctors have seen no increase in reportable diseases and there is no risk of an outbreak associated with dead bodies, said PAHO Deputy Director Jon Andrus.

Reports of mass graves were disheartening, he said, but the United Nations was working to get bodies to a central location for identification and family follow-up.

"If we were to be self-reflective, I think we're not satisfied at all," Andrus said. "Conditions are incredibly challenging. But I can tell you that we are doing our very, very best, despite these difficult conditions."

U.N. Secretary-General Ban Ki-moon said he couldn't predict how long it would take to get the aid already collected for Haiti flowing freely into the country.

The United Nations has 9,000 peacekeepers in Haiti -- 3,000 of them in the capital -- and Ban has requested that the U.N. Security Council increase levels by an additional 3,500 "to take charge of all this security, to help humanitarian assistance be delivered in a safe way."

The United States has 1,400 military forces in Haiti and an additional 5,000 offshore, Keen told reporters Monday. That will grow to 4,000 to 5,000 in Haiti, with an additional 5,000 in support, he said.

Meanwhile, the search for survivors continued. Rescuers have pulled more than 75 people from under rubble, Merten said, and more survivors were still being found.

A CNN crew in the Haitian capital Monday witnessed workers pulling a university student from a flattened school. Text messages sent from beneath the rubble had drawn rescuers to the scene, said paramedic Clever Sobrino, who added that more survivors were thought to be trapped inside.

No overall death toll has been declared; estimates range from 100,000 to 150,000 in Port-au-Prince alone.

CNN's Anderson Cooper, Susan Candiotti, Rich Phillips, Arthur Brice, Eric Marrapodi and Chris Lawrence contributed to this report.