TOKYO (Reuters) - A worker at Japan's destroyed Fukushima nuclear power plant died on Tuesday after falling inside a water storage tank, the latest in a spate of industrial accidents at the site of the March 2011 nuclear disaster, the world's worst since Chernobyl.

The death is the second in Fukushima in less than a year. Last week, labor inspectors warned the operator of the plant, Tokyo Electric Power Company (Tepco), about the rise in accidents and ordered it take measures to deal with the problem.

The unnamed laborer in his 50s working for construction company Hazama Ando Corp. on Monday fell into a 10m-high water storage tank he had been inspecting. The tank was empty at the time and the worker died on Tuesday after being taken to a local hospital, said Tepco.

"We are deeply sorry for the death of the worker and express our deepest condolences to the family. We promise to implement measures to ensure that such tragedy does not occur again," Mr Akira Ono, the head manager of the Fukushima plant, said in a statement. Hazama Ando had no immediate comment.

The number of accidents at the Fukushima plant, including heatstrokes, has almost doubled this fiscal year to 55. The increase came as Tepco ramped up clean-up efforts and doubled the number of workers at the site to nearly 7,000.

In March, a worker at the Fukushima plant died after being buried under gravel while digging a ditch.

In a separate accident on Tuesday morning, a worker at the Fukushima No. 2 nuclear power plant, a sister plant of the wrecked Fukushima No. 1 station, was injured and lost consciousness while inspecting equipment at a facility sorting radioactive waste, Tepco said.

The worker was taken to a nearby hospital by helicopter this morning, the plant operator said, adding he was not exposed to radiation.

Fukushima No. 2 is located some 15km to the south of the destroyed Fukushima No. 1 plant. The complex has served as a hub for companies and workers involved in the cleanup of the Fukushima No. 1 plant.

Tepco has been widely criticised for its handling of the cleanup. Until last year it struggled to contain leaks of radioactive water from hastily built tanks at the site, and it has repeatedly promised to improve working conditions.

Most workers inside the plant are contract laborers hired by multiple layers of construction companies.

A Reuters investigation in 2013 found widespread labour abuses, including workers who said their pay was skimmed and that there was little scrutiny of working conditions at the plant. "It's not just the number of accidents that has been on the rise. It's the serious cases, including deaths and serious injuries that have risen so we asked Tokyo Electric to improve the situation," said Mr Katsuyoshi Ito, a local labour inspector overlooking the Fukushima power plant.

Ito said inspectors were investigating the recent death.