SOMA, Japan — A fire broke out at a nuclear reactor again Wednesday, a day after the power plant emitted a burst of radiation that panicked an already edgy Japan and left the government struggling to contain a spiraling crisis caused by last week’s earthquake and tsunami.

The outer housing of the containment vessel at the No. 4 unit at the Fukushima Dai-ichi nuclear complex erupted in flames early Wednesday, said Hajimi Motujuku, a spokesman for the plant’s operator, Tokyo Electric Power Co.

On Tuesday, a fire broke out in the same reactor’s fuel storage pond — an area where used nuclear fuel is kept cool — causing radioactivity to be released into the atmosphere. Tokyo Electric Power said the new blaze erupted because the initial fire had not been fully extinguished.

About three hours after the blaze erupted Wednesday, Japan’s nuclear safety agency said fire and smoke could no longer be seen at Unit 4, but that it was unable to confirm that the blaze had been put out.

Also Wednesday, Japan’s nuclear safety agency said 70 percent of the nuclear fuel rods may have been damaged at another Fukushima Dai-ichi reactor that was first stricken last week, triggering the crisis.

“But we don’t know the nature of the damage, and it could be either melting, or there might be some holes in them,” said an agency spokesman, Minoru Ohgoda.

Japan’s national news agency, Kyodo, said 33 percent of the fuel rods at a second reactor were also damaged.

Radiation levels in areas around the nuclear plant rose early Tuesday afternoon but appeared to subside by evening, officials said. But the unease remained in a country trying to recover from the massive disasters that are believed to have killed more than 10,000 people and battered the world’s third-largest economy.

The radiation leak caused the government to order 140,000 people living within 20 miles (30 kilometers) of the plant to seal themselves indoors to avoid exposure, and authorities declared a ban on commercial air traffic through the area. Worries about radiation rippled through Tokyo and other areas far beyond that cordon. The stock market plunged for a second day, dropping 10 percent.