The higher rating is an open acknowledgement of what was widely understood already: The nuclear accident at the Fukushima Dai-ichi plant is the second-worst in history. It does not signal a worsening of the plant's status in recent days or any new health dangers.

Still, people living nearby who have endured a month of spewing radiation and frequent earthquakes said the change in status added to their unease despite government efforts to play down any notion that the crisis poses immediate health risks.

Miyuki Ichisawa closed her coffee shop this week when the government added her community, Iitate village, and four others to places people should leave to avoid long-term radiation exposure. The additions expanded the 12-mile (20-kilometer) zone where people had already been ordered to evacuate soon after the March 11 tsunami swamped the plant.

"And now the government is officially telling us this accident is at the same level of Chernobyl," Ichisawa said. "It's very shocking to me."

Japanese nuclear regulators said the severity rating was raised from 5 to 7 on an international scale overseen by the International Atomic Energy Agency due to new assessments of the overall radiation leaks from the Fukushima Dai-ichi plant.