TOKYO — Tokyo Electric Power Co. (Tepco), the utility that operates the Japanese nuclear plant devastated two years ago by an earthquake and tsunami, is scrambling to build more tanks to safely store radioactive water after leaks were found at makeshift pits.

Workers at the Fukushima Daiichi plant have so far filled up more than 80 percent of the 325,000 tonnes of available storage with groundwater contaminated by the damaged nuclear reactors.

Leaks in the current water transfer and storage system have added to the urgency to expand this capacity: on Thursday, the utility known as Tepco said pipes used to transfer radioactive water from a leaking pit burst in what is the fourth leak in less than a week.

"We've been told it's an emergency situation and we have to speed up the construction of the water tanks any way we can," said a worker at the plant who declined to be named as he is not authorized to speak to the media.

"There are a lot of makeshift fixes. They are walking a tightrope from one jerry-rigged fix to another," he said at the site, now a cluster of ramshackle buildings and exposed steel girders on Japan's northeastern coast.

On Wednesday, Tepco president Naomi Hirose said the utility would transfer all the contaminated water currently stored in the makeshift pits to reinforced tanks by early June.

A Tepco spokeswoman on Thursday confirmed the utility was planning to build new tanks, but declined to be more specific.

The utility currently has 933 reinforced steel tanks with a maximum capacity of 1,100 tonnes, while 5 out of 7 massive pits lined with plastic sheeting still hold toxic water.

Tepco has struggled with the clean-up of Fukushima, site of the world's worst nuclear disaster in 25 years, since a magnitude 9.0 earthquake and tsunami knocked out power and cooling to the station, causing meltdowns in three reactors.

Recent mishaps, including two power outages, have heightened concerns about Fukushima's stability and called into question Tepco's ability to decommission the plant.

Renewed radiation fears could also scuttle Tokyo's hopes to be chosen as the host city of the 2020 Olympic Games.

"The issues are just snowballing. Tepco cannot do this alone, but the government, the regulator, they all refuse to take responsibility," said Masashi Goto, a retired nuclear engineer and industry expert.

Tepco's Hirose, however, has rebuffed suggestions that the utility needs outside help.

Last month, Tepco lost vital power used to cool spent uranium fuel rods in pools in the complex. The utility later said the 29-hour power outage was caused by a rat that shorted a temporary switchboard.

Two weeks later, workers attempting to install a net to block rodents tripped the same system again.

The Asahi Shimbun, one of the biggest newspapers in Japan, called the Fukushima plant "a toxic water production facility" in an editorial this week. It also urged the government to take a more active role in the plant's decommissioning.