Pakistan ? U.S. Army choppers flew their first relief missions in Pakistan’s flood-ravaged northwest Thursday, airlifting hundreds of stranded people to safety from a devastated tourist town and distributing emergency aid.

In the country’s south, authorities began evacuating half a million people as the worst monsoon rains in decades threatened new destruction.

The floods have already killed an estimated 1,500 people over the past week, most in the northwest, the center of Pakistan’s fight against al-Qaida and the Taliban. An estimated 4.2 million Pakistanis have been affected, including many in eastern Punjab province, which has seen numerous villages swallowed by rising water in recent days.