DEHRADUN, India — Ever since flash floods struck a mountainous area of northern India last week, 60 Indian military and civilian helicopters have been navigating fog, rain and treacherous Himalayan valleys looking for survivors and recovering bodies as part of the biggest airborne rescue and recovery operation in the history of the Indian military.

As of Tuesday, the operation had rescued more than 12,000 people, many of them Hindu pilgrims visiting holy shrines in the state of Uttarakhand, one of the worst-hit areas. The flooding, which began June 16, triggered by monsoons, has killed at least 1,000 and possibly many hundreds more.

But the rescue operation is not without hazards of its own. On Tuesday afternoon, a Russian-made Mi-17 air force helicopter crashed into a mountain, killing 19 aboard — 5 airmen and 14 paramilitary members — while returning from a mission in the Kedarnath Valley, a major pilgrimage center more than 11,000 feet above sea level, a spokesman for one of India’s paramilitary groups said. Last week, another helicopter crashed in the same area, although no one died.

Pilots say the difficult terrain, adverse winds and absence of landing pads are testing their will and courage. “It is a warlike situation for us,” said one pilot, Capt. Sandeep Soti. “We have been pushing our men and our machines beyond our capacities.”