Japan is considering raising the severity level of its nuclear crisis from 5 to the maximum 7.

That would be the same as for Chernobyl 25 years ago, the worst atomic power disaster in history.

Experts say at least seven cores or pools have been in difficulty, but at Chernobyl it was only one reactor that created the problem.

The government also expanded an evacuation zone around the crippled Fukushima nuclear plant because of high levels of accumulated radiation.