New Delhi, June 30 -- With the window for finding survivors shrinking fast, Venezuelans combed Monday through more ruins of buildings toppled by last week's powerful back-to-back earthquakes, and attention turned to the country's humanitarian crisis that could persist for years.

Relief organizations say the first 72 hours after a natural disaster is the most crucial time period for rescues, though survival can be extended if people have access to food and water. Five days after the twin quakes, questions loomed about whether the cash-strapped government will be able to coordinate the effort needed to care for thousands of people who have been left homeless.

In other developments, a 4.6 magnitude aftershock rumbled through the disaster z...