SHANGHAI—China halted approvals of new nuclear-power plants pending changes to safety standards, signaling a shift toward caution from a country embarked at high speed on the world's biggest expansion program but where public nervousness is growing as a disaster unfolds in neighboring Japan.

The government also ordered integrity checks at existing plants. China has 13 nuclear reactors in operation, at least 25 more under construction, and a five-year plan adopted by the National People's Congress just this month contains approvals...