Pakistani and U.S. military helicopters delivered aid at a brisk pace to the earthquake-stricken region of Kashmir on Tuesday amid warnings from the World Food Program that a half-million survivors have yet to receive desperately needed help.

Choppers landed under sunny skies in Muzaffarabad (search), the capital of Pakistan's portion of the divided Kashmir region, bringing tents and other supplies, while relief workers set up field hospitals to treat thousands of stranded, injured people.

Authorities warned that exposure and infections could drive the death toll up from 54,000 as the harsh Himalayan winter loomed. Landslides caused by the 7.6-magnitude earthquake on Oct. 8 cut off many roads, and they could take weeks to clear.

The relief effort is one of the most challenging the world has ever faced, according to James Morris, executive director of the U.N. World Food Program (search).

"The aid agencies have managed to give some help to hundreds of thousands of people, but there are an estimated half a million more people out there in desperate need, who no one has managed to reach," Morris said from Dubai. "People don't just need food — first of all they need shelter, blankets and medical assistance — then food and clean water."

The WFP said hundreds of villages still had received no help, and that thousands of lives were at stake. Morris said temperatures are dropping, raising the risk of hypothermia among survivors. He warned there is "very little time left" to avoid further catastrophe.

Maj. Farooq Nasir, an army spokesman, said smaller helicopters would take relief goods brought by big choppers to forward bases in the Neelum and Jhelum valleys on to remote mountain villages.

The United Nations said more than 80 helicopters were flying, and that the world body was planning to send up to 150,000 tents for the homeless, in addition to about 30,000 already distributed.

It said field hospitals with operating theaters were being set up, improving the survival chances for those requiring urgent surgery, but that the large numbers of patients were still "overwhelming."

Keith Ursel, Muzaffarabad operations head for the World Food Program, said hundreds of villages had not received aid, and that thousands of lives were at stake.

"We need 570 tons of food every day to feed the affected people stranded in these villages," he said. "It is always a mixture of starvation, wounds or rough weather and fear which lead to massive deaths in such a situation."

Most of the deaths were in Pakistani-controlled Kashmir (search), while 1,360 people died in the Indian-held part of the divided region.

India has provided some aid to Pakistan, but turned down a Pakistani suggestion that it send military helicopters — without crews — to help with relief work. Pakistan, which has fought two of its three wars with India over Kashmir, said it could not have the Indian military involved directly in relief efforts.

Some 80,000 people were injured in the quake. The United Nations has estimated 3.3 million were left without homes and need food and shelter ahead of the approaching winter, with snow already falling in some affected areas.

Maj. Gen. Farooq Ahmed Khan, Pakistan's top relief official, said 33,000 tents and 130,000 blankets have been distributed. He said 260,000 tents and 2 million blankets were needed.

Pakistani President Gen. Pervez Musharraf (search) traveled by helicopter on Tuesday to the Kashmiri town of Bagh, where he met earthquake victims with broken limbs and other injuries. He said shelter was a priority.

"We gave all the tents that the army had. We bought all that were in Pakistan. Now we are looking abroad, in the international community," Musharraf said.

Maj. Gen. Shaukat Sultan, Pakistan's chief army spokesman, said relief workers were expected to reach all affected villages in the next few days, although he acknowledged that many places that have received aid might not have adequate shelter. He said another 24 U.S. military Chinook helicopters were expected to arrive in about a week to assist in relief efforts.

Eighty Pakistani soldiers were flown by helicopter into the Neelum Valley, about 15 miles northeast of Muzaffarabad, to carry emergency rations and other relief supplies on foot to those in need, the army said.

Soldiers also drove mule teams with relief supplies to some of the region's steep-sided villages, crossing people with bundles on their shoulders carefully walking down to lower elevations.

The U.N. International Labor Organization warned that more than 1.1 million jobs may have been lost as a result of the earthquake, adding that employment programs were urgently needed to lift millions of people out of poverty deepened by the disaster.

There were some signs of normalcy returning to Muzaffarabad on Tuesday, amid the devastation. Some shops reopened for business, and a military-run telecommunications company set up camps where residents can make telephone calls or send e-mails and faxes, free of charge.