KATMANDU, Nepal — A steel footbridge collapsed yesterday in western Nepal under the weight of hundreds of people on their way to a fair, plunging scores about 100 feet into icy Himalayan waters. At least 15 were killed and more than 100 were missing and feared dead, officials said.

Troops were being rushed to the area to assist with search-and-rescue operations. But with efforts halted by nightfall, hopes were slim of finding more survivors in the fast-flowing mountain river, the top government official in the area, Anil Pandey, said.

Authorities believe some 500 people traveling to a village fair were crossing the Bheri River on the bridge when its support cables snapped under the weight, Mr. Pandey said.

“Some of them managed to climb to safety, some fell on the banks, but the ones who plunged in the river are the ones who are still missing,” he said.

Crowds gathered on both sides of the river, trying to save the victims and treating the wounded. Some of those who had fallen used the bridge’s cables to haul themselves up.

By nightfall, rescuers had recovered 15 bodies, while 32 seriously injured victims were flown to hospitals in more developed parts of the country, said Dipendra Chetri, a police official who helped rescue people in Chunchu, the village where the bridge collapsed.

“It is hard to say how many people are missing, but the best estimate I can say is more than 100 people could be missing,” another police officer, Purushottam Khatri, said.

Authorities feared there could be many more casualties because the river has strong currents and is difficult to swim. Searches would resume at daybreak today, Mr. Pandey said.

Complicating the accounting was the remoteness of the accident scene.

Chunchu is about 310 miles west of Katmandu in a rural part of this Himalayan country with few paved roads. The most common way of traveling is by foot or oxcart.

Much of the impoverished region’s already-poor infrastructure was devastated by the decade-long communist uprising that ended last year. The Maoist rebels, who controlled much of the area, would frequently blow up bridges and roads to impede government troop movements.

Mr. Pandey said the 400-foot-long bridge was built this year. However, it was not designed to hold the weight of so many people crossing at once.

The fair attracts thousands of people from surrounding villages. It is held every month after the full moon.