According to the AFP news agency, Prime Minister Yoshihiko Noda told a meeting of his nuclear taskforce that the reactors "have reached a state of cold shutdown to the point where the accident is now under control."
The stabilization of the power plant comes nine months after a combined earthquake and tsunami damaged the reactors, causing them to discharge radioactive particles into the air and sea.
Parts of the evacuation zone around Fukushima remain polluted, with the clean-up proceeding slowly.
The BBC has cited the Japanese government as saying it could take up to 40 years to fully decommission the plant and clean up surrounding areas.
compiled from agency reports