A worker at the stricken Fukushima Daiichi nuclear power plant has died after falling into an empty water storage tank, in the latest of a series of accidents at the site of the worst nuclear disaster for a quarter of a century.

The death was the second at Fukushima Daiichi in less than a year, but the plant’s operator, Tokyo Electric Power (Tepco), insisted that it was doing everything possible to prevent accidents.

Almost 7,000 workers are involved in decommissioning Fukushima Daiichi, which suffered a triple meltdown after it was struck by a powerful earthquake and tsunami in March 2011.

Removing melted fuel and dismantling the ruined facility is expected to take four decades.

The latest death there, of an unnamed man in his 50s, comes days after inspectors visited the plant and ordered Tepco to address the rising number of accidents. Last March, a worker died after being buried by gravel while digging a ditch.

In a separate incident on Tuesday, a worker in his 40s died in hospital after equipment fell on him at a facility storing radioactive waste at the nearby Fukushima Daini plant, Kyodo News said. The plant, which escaped serious damage from the tsunami, is being used as a hub for companies involved in decommissioning.

The number of injuries, excluding cases of heatstroke, has almost doubled in the past two years. In fiscal 2013 Tepco recorded 23 injuries, while the number between April and November last year had already reached 40.

The firm attributed the rise to an increase in the average number of workers at the site during weekdays, from 3,000 early last year to almost 7,000 today.

“We are taking all sorts of measures to prevent accidents,” a Tepco spokeswoman said. They include training sessions for Tepco employees and workers hired by the firm’s many contractors on how to spot potentially dangerous situations at the plant, which now resembles a huge construction site

The Fukushima Daiichi worker died after falling into a 10-metre-tall storage tank he was inspecting on Monday. He was taken to hospital but died early on Tuesday.

“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,” Akira Ono, the manager of Fukushima Daiichi, said in a statement.

The man’s employer, the construction firm Hazama Ando, had no immediate comment.

In response to concerns that lack of proper rest was making Fukushima Daiichi workers more susceptible to lapses in concentration, Tepco will open a new facility in March where up to 1,200 workers at a time can rest and have meals.

Several firms recently created a new company that will provide nutritious meals for about 3,000 workers a day from April.

Most Fukushima Daiichi workers belong to a vast network of contractors in the construction industry that are helping Tepco decommission the facility.

Amid accusations that some unscrupulous firms were withholding mandatory hazard allowances from their employees, four former and current workers last September took Tepco and several of its partner firms to court seeking $600,000 in unpaid wages.

“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,” Katsuyoshi Ito, a local labour standards inspector told Reuters.