Japanese prosecutors have questioned the former head of the operator of the Fukushima power plant on suspicion of negligence over the nuclear crisis, local media reported Thursday.

Tsunehisa Katsumata, who was Tokyo Electric Power Co (TEPCO) chairman when the plant was crippled by the March 2011 earthquake and tsunami, was questioned on a "voluntary basis," news agencies, dailies and TV networks said.

Investigators in Fukushima and Tokyo were acting on a criminal complaint filed last year by a group of citizens against about 40 people including Katsumata and former TEPCO president Masataka Shimizu, the reports said.

Critics say Katsumata and other TEPCO executives failed to take measures after the company estimated in 2008 that the plant was vulnerable to a tsunami higher than 15 metres (50 feet), the reports said.

TEPCO was reportedly prepared only for waves six metres high.

The complaint said the accused were responsible for causing evacuees to die and for many evacuees to suffer injuries through exposure to radiation.

Katsumata, 72, served as TEPCO president between 2002 and 2008 and as its chairman between 2008 and 2012. He left its board in June last year.

The prosecutors are expected to decide in a few months whether to file criminal charges against Katsumata and the others.

But many prosecutors believe it will be difficult to establish any causal relationship between the nuclear disaster and the deaths and injuries among evacuees, Kyodo News said.

They also question whether it was reasonably possible for TEPCO executives to predict the unprecedented scale of the tsunami.

A 9.0-magnitude tremor struck off Japan's northeast coast, triggering monster waves that surged ashore at heights of up to 40 metres.

The double disaster killed nearly 19,000 people and crippled the Fukushima plant's cooling systems, sparking reactor meltdowns and radiation leaks.

Tens of thousands of people have been evacuated from around the plant.

Under Japan's penal code a conviction for professional negligence resulting in death or injuries could result in imprisonment for up to five years or a fine of one million yen ($11,300), Kyodo said.