Update at 7:21 p.m. ET: Residents within a 2-mile radius of the Fukushima No. 2 plant have been ordered to evacuate, the government has announced.

Here's the utility's latest update on the troubles at its overheating nuclear plants.

Update at 6:36 p.m. ET: The Japanese government has declared a nuclear emergency at the Fukushima No. 2 power plant (Daini). An emergency also exists at plant No. 1 (Daiichi).

Original post: The cooling system has failed for three reactors at the Fukushima No. 2 nuclear plant, about seven miles from its quake-crippled companion, the Tokyo Electric Power Co. now says.

The utility, which operates both Fukushima plants, notified the government Saturday morning that the failsafe system at the No. 2 plant stopped working as the coolant water topped the boiling point, the Kyodo news service reports.