KATMANDU, Nepal — Bikash Suwal, a lithe, tanned Nepali trekking guide, has climbed the 18,805-foot Yala Peak in the towering Himalayas. But since a powerful earthquake rocked Nepal a week ago, he has been afraid to climb the stairs to the rented rooms he shares with five family members.

Like many of his neighbors in the usually thrumming Gongabu area of Katmandu, Mr. Suwal fears that the buildings still standing are so poorly constructed that they may be toppled by aftershocks.

“A mountain is safer than this,” he said Wednesday of the four-story concrete and brick building where he lives. “Up there, climbing, I sometimes feel afraid, but not like this. This kind of danger is not in my hands.”

Jittery fear has coursed through Nepal’s storied capital, Katmandu, since Saturday’s quake, which is thought to have killed more than 6,250 people across Nepal. Ancient temples in Katmandu crumpled from the intense pulses of seismic energy that the earthquake unleashed, but so did many dozens of buildings constructed after a modern building code was put in place.