Authorities discovered highly radioactive water leaking from the crippled Fukushima Daiichi nuclear plant into the ocean Saturday, the latest sign that the desperate strategies being used to cool the overheating reactors could be creating new problems.

The toxic water had pooled by an almost eight-inch-long crack in the concrete wall of a pit at the unit-2 reactor where power cables are stored, Japan’s nuclear regulatory office said. The radioactivity level in the air above the water was measured at 1,000 millisieverts per hour, four times the maximum level that workers can be exposed to under Japanese law.

Emergency crews poured concrete into the crack Saturday afternoon and again in the evening in a bid to stem the leak, the Yomiuri Shimbun newspaper reported. However, the concrete was unable to set because the water washed it away, authorities said, and Tokyo Electric Power Co., which operates the plant, was considering using a plastic polymer Sunday morning.

Hidehiko Nishiyama, deputy director general of Japan’s Nuclear and Industrial Safety Agency, said the government has instructed Tepco to examine the facility for other potential leaks.

“Today we found highly irradiated water in the pit where the electricity cables are contained,” Nishiyama said at a news conference. “It seems that there is a crack on the side of the concrete wall of the pit. Some water is spilling out of the crack to the sea.”

The discovery raised the disconcerting possibility that the power company’s decision to drench the reactors with tens of thousands of tons of water in an attempt to submerge the exposed spent fuel rods is having an unintended side effect.

Workers have scrambled to try to figure out what to do with the irradiated water that has built up in the plant. They have put some in storage tanks and moved some into floating barges offshore. Yet three workers laying power cables at the plant two weeks ago suffered leg burns after stepping in a highly toxic pool of water; they were released from a radiation hospital this week after doctors concluded they had not suffered long-term damage.

Government officials said they had not determined the source of the radiation in the water that was found leaking Saturday.

“We will investigate the route the water is flowing into the pit,” Nishiyama said.

The setback undercut any momentum Prime Minister Naoto Kan had hoped to build when he announced Friday that the government would turn its attention to recovery and reconstruction.

Kan, making his first visit to areas affected by the March 11 earthquake and tsunami, traveled in a Japanese military helicopter to Rikuzentakata in northern Iwate prefecture, which had been hit hard by the twin disasters. In the city of 23,000, more than 1,000 people are dead and 1,000 others remain missing, with 13,000 living in shelters, said Noriyuki Shikata, a government spokesman.

All told, 11,938 people were killed by the quake and tsunami, and 15,478 are missing, according to the National Police Agency. The Japan Self-Defense Forces, with the help of the U.S. military, will finish a three-day intensive search for bodies Sunday. So far, they have found 66 bodies over two days, according to Kyodo News.

Kan saw “mountains of debris and rubble, basically ruins,” Shikata said. The prime minister then visited the nuclear plant workers at a staging area about 12 miles from the plant, he added.

Two employees at the damaged nuclear power plant, who had been missing since the March 11 triple disasters, were confirmed dead on Sunday by Tepco.  The bodies of Kazuhiko Kokubo, 24, and Yoshiki Terashima, 21, were found in the basement of the turbine buildings outside of the unit-4 reactor on March 30, company officials said. 

"We feel extreme remorse about losing our young employees, who, while being attacked by earthquake and tsunami, tried to protect the safety of the plant," officials said in a news release. 

Four workers were also injured at the plant during the earthquake and tsunami, according to an April 1 report by the Nuclear and Industrial Safety Agency; two have already returned to work. Since then, 21 workers have been treated for other injuries, including 15 who were injured during the hydrogen explosions in the unit-1 and unit-3 reactors.  Seven of those injured are subcontractors for the power company and four are members of Japan's Self-Defense Force.

Meanwhile, Japan continued to receive aid from other countries, including a German-designed robot that can be used to remove debris and help repair the power plant; British radiation counters and gas masks; and 10,000 tons of gas and diesel from China. A 15-member advance team from the U.S. military’s radiation control squadron arrived at Yokota Air Base, to be followed by 140 Marines who are trained to screen for radiation and prevent contamination.

Of the 32 foreign embassies in Tokyo that had suspended operations after the earthquake, 18 have reopened, Foreign Ministry spokesman Takeshi Matsunaga said.

Staff writer Michael Alison Chandler contributed to this report.