PORT-AU-PRINCE (Reuters) - A new earthquake shook the devastated Haitian capital Port-au-Prince early on Wednesday, rattling already wrecked buildings and triggering panic among survivors of last week’s devastating quake.

The largest aftershock since the killer quake struck on January 12 alarming masses of people camping on the streets. But it did not appear to cause any new destruction or to slow the international relief effort, bolstered by more U.S. troops.

The aftershock hit at daybreak and was first estimated at 6.1 magnitude, then revised to 5.9. Shrieking Haitians ran from buildings and walls, fearing a repeat of the magnitude 7 quake that killed tens of thousands of people eight days ago.

“Things started shaking. We were really afraid. People came out into the street,” said Victor Jean Rossiny, a law student living in the street. “We have nothing here, not even water.”

Desperate and hungry residents of Port-au-Prince have been sleeping outdoors because their homes were destroyed last week or out of fear of aftershocks.

Violence and looting has subsided as U.S. troops provided security for water and food distribution, and thousands of displaced Haitians heeded the government’s advice to seek shelter outside Port-au-Prince.

Haitian officials estimated the death toll from last week’s quake could be between 100,000 and 200,000, and said 75,000 bodies had already been buried in mass graves.

U.S. Black Hawk helicopters landed in the grounds of Haiti’s wrecked presidential palace, deploying troops and supplies and immediately attracting crowds of survivors who clamoured for handouts of food.

“Supplies are beginning to get out to the people,” U.S. Defense Secretary Robert Gates said while visiting India. ” ... My hope is that as we get these trucks out on the roads with supplies and people see patrols -- that will prevent any significant violence from taking place.”

AMPHIBIOUS LANDING

U.S. Marines in landing craft brought ashore bulldozers, mechanical diggers and trucks on a beach at Neply village west of Port-au-Prince from warships anchored offshore.

Pack-laden troops on the beach handed out food rations and set up temporary shelters for the homeless. Crowds of Haitians quietly watched as the Marines set up a forward base in the grounds of an old mission school, pitching rows of tents flanked by a row of latrines.

At the airport in the damaged coastal city of Jacmel, Sri Lankan, U.S. and Canadian troops delivered supplies.

Traffic congestion in Port-au-Prince was worse than ever on Wednesday -- perhaps a small sign of recovery -- as aid trucks and locals drove to gasoline stations to fill their tanks, jamming streets still cluttered with earthquake debris.

Fuel prices have doubled and there were long lines of cars, motorbikes and people with jerrycans outside gas stations.

Cash needs to start circulating again in Haiti’s shattered economy so people can buy food and civil servants can be paid, an International Monetary Fund official said.

Banks would reopen shortly and money transfer agencies were beginning to process remittances from Haitians living abroad, Nicolas Eyzaguirre, director of the IMF’s Western Hemisphere Department, said on the fund’s website.

Remittances total about $1.8 billion a year, accounting for at least 20 percent of Haiti’s gross domestic product, economists say.

“Many people tell me they have run out of cash or are about to,” said Simon Schorno, spokesman for the International Committee of the Red Cross in Port-au-Prince.

The city’s water system was only partially functional but tanker trucks began to deliver water to the larger makeshift camps, where vendors did brisk business selling charcoal to families who were using small tin barbecues to cook.

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LOCALIZED VIOLENCE

Landline telephones in Port-au-Prince were still down, but two wireless networks had spotty service, said U.S. Federal Communications Commission officials helping with the relief.

While military escorts are needed to deliver relief, the United Nations said security problems were mainly in areas considered “high risk” before the disaster.

“I have seen no indications that leads me to believe that the security situation is deteriorating,” said General Floriano Peixoto, chief of the Brazilian U.N. peacekeeping contingent.

Brazilian peacekeepers have helped Haitian police recapture some of the 4,000 prison inmates who escaped in the quake.

To speed the arrival of aid and stem looting and violence, the U.N. Security Council has unanimously agreed to temporarily add 2,000 U.N. troops and 1,500 police to the 9,000-member peacekeeping mission in Haiti.

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Around 12,000 U.S. military personnel are on the ground in Haiti and on ships offshore including the U.S. Navy hospital ship Comfort, which arrived on Wednesday to provide essential capacity for complex surgeries.

At least one Latin American leader, Venezuela’s socialist President Hugo Chavez, a persistent critic of what he calls U.S. “imperialism,” has already accused Washington of “occupying” Haiti under the pretext of an aid operation.

Haitian President Rene Preval has said U.S. troops will help U.N. peacekeepers keep order in Port-au-Prince.

MEDICINE URGENTLY NEEDED

So far, feared outbreaks of infectious diseases have not erupted, although many of the injured faced the immediate threats of tetanus and gangrene.

Hospitals were overwhelmed and doctors lacked anaesthesia, forcing them to operate with only local painkillers.

Doctors Without Borders said a cargo plane with 12 tons of medical supplies had been turned away from the congested Port-au-Prince airport three times since Sunday, and five patients died for lack of the supplies it carried.

“We were forced to buy a saw in the market to continue amputations,” said Loris de Filippi, emergency coordinator for the group’s Choscal Hospital in Cite Soleil.

International search and rescue teams were still combing rubble for survivors and had pulled 121 people from collapsed buildings, a record for the number rescued after an earthquake, the Pan-American Health Organisation said.

The World Food Program had provided 200,000 people with rations for seven days, but the International Organisation for Migration estimated that 200,000 families -- or one million people -- were in need of immediate shelter.

Many people were surviving on high-protein biscuits or dry emergency rations. The Food for the Poor charity managed to reopen its kitchens in Port-au-Prince and served up vats of rice, beans and chicken, giving thousands of people their first hot meal in more than a week.