TOKYO (AP) - Japan's nuclear safety agency says it's raised the severity rating of the country's nuclear crisis after discovering evidence of a partial meltdown.

The agency says officials declared it a level 5 event after they realized that at least 3 percent of the fuel in three of the reactors at the Fukushima Dai-Ichi plant had been severely damaged. That suggests those reactor cores have partially melted down and thrown radioactivity into the environment.

The situation had been classified as a level 4 on the international nuclear event scale, defined as having local consequences.

A level 5 puts it on a par with the 1979 Three Mile Island accident. The hallmarks of a level 5 emergency are severe damage to a reactor core, release of large quantities of radiation with a high probability of “significant” public exposure or several deaths from radiation.

The 1986 Chernobyl accident was a level 7, the highest on the scale. At least 31 people died of radiation sickness in that disaster, which spewed radiation for hundreds of miles.
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