Prosecutors in the only criminal trial involving the 2011 Fukushima nuclear plant meltdown have appealed against the acquittal of three former Tokyo Electric Power Co executives.

The Tokyo District Court on September 19 found ex-Tepco chairman Tsunehisa Katsumata and two others not guilty of professional negligence in the disaster and the death of 44 elderly patients who were forcibly evacuated from local hospitals.

Japan Nuclear Disaster
(From left) Tsunehisa Katsumata and vice presidents Sakae Muto and Ichiro Takekuro were all acquitted (Satoru Yonemaru/AP)

The court said a tsunami of the size that hit the plant after an earthquake was unpredictable and the executives were not required to take preventive measure or to stop the reactors under government safety standards.

Lawyers representing thousands of disaster-hit residents said the prosecution appealed against the verdicts on Monday.

The prosecution had demanded five-year prison terms.