TOKYO—Crucial efforts to tame Japan's crippled nuclear plant were delayed by concerns over damaging valuable power assets and by initial passivity on the part of the government, people familiar with the situation said, offering new insight into the management of the crisis.

Meanwhile, a regulator who was inspecting the Fukushima Daiichi nuclear-power complex when the quake hit offered The Wall Street Journal one of the first eyewitness accounts of the havoc at the site, describing how the temblor took...