Tensions are mounting in Haiti as help trickles in. Reports of looting and human bodies as roadblocks.

The situation gets worse by the hour!

PORT-AU-PRINCE, Haiti — Conditions in this earthquake-ravaged nation grew more dire on Friday morning as rescuers raced against time to find anyone still alive beneath mountains of rubble while aid workers struggled to deliver relief supplies to survivors increasingly desperate for food and clean water.

In signs of rising tensions, looters in Haiti’s capital broke into United Nations food warehouses that had been stocked with 15,000 tons of provisions, and a photographer for Time magazine told Reuters that residents had created two makeshift roadblocks by piling up bodies and debris.

Meanwhile, the first wave of American troops arrived overnight to begin handling security and cargo operations at Haiti’s main airport, and more soldiers and Marines were expected to fly into the country later on Friday.

“The main thing is to try to establish some order at the airport so we can start getting planes in and out,” said Col. Patrick Hollrah of the Air Force, whose disaster-response team arrived Thursday night from New Jersey aboard a C-17 cargo plane.

In the cockpit of the plane, air traffic chatter could be heard through headsets, giving some sense of the barely controlled confusion in the skies. Planes were being forced to circle for two to three hours before landing.

Also Thursday night, the United States reached an agreement with Cuba to allow American planes on medical-evacuation missions to pass through restricted Cuban airspace, a White House official said, reducing the flight time to Miami by 90 minutes.

The Haitian president, René Préval, said that 7,000 people had already been buried in a mass grave. Hundreds of bodies piled up outside the city’s morgue, next to a hospital. On street corners, people pulled their shirts up over their faces to filter out the thickening smell of the dead. Meanwhile, doctors and search-and-rescue teams worked mostly with the few materials on hand and waited, frustrated, for more supplies, especially much-needed heavy equipment.

“Where’s the response?” asked Eduardo A. Fierro, a structural engineer from California who had arrived Thursday to inspect quake-damaged buildings. “You can’t do anything about the dead bodies, but inside many of these buildings people may still be alive. And their time is running out.”

A number of nations pledged financial aid, deployed rescue teams and loaded cargo planes with food and supplies. Jean-Bertrand Aristide, Haiti’s former president who was ousted five years ago, wept Friday as he told The Associated Press in Johannesburg that he and his family wanted to return and “help rebuild the country.” Relief agencies broadcast appeals and assembled their own aid teams; and Web sites were set up to connect people overseas with friends and family in Haiti.

But United Nations officials said that Haitians were growing hopeless — and beginning to run out of patience.

Meanwhile, the situation at the airport is no better, as dozens of planes are in the tarmac, without fuel and unloaded.

More as it comes in.