The UN World Food Program on Tuesday warned that half a million earthquake survivors have yet to receive relief supplies, and Pakistan's president said during a visit to a quake-stricken town that he had appealed to the international community for more tents to shelter the homeless. Under sunny skies, Pakistani and US military helicopters delivered aid at a brisk pace to Muzaffarabad, the capital of Pakistan's portion of the divided Kashmir region, which suffered most of the damage and casualties from last week's massive earthquake. Relief workers rushed to set up field hospitals to treat thousands of stranded, injured people. The relief effort is one of the most challenging the world has ever faced, according to James Morris, executive director of the WFP. The WFP said hundreds of villages had not yet received help. Heavy rains on Sunday grounded many relief flights. 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.