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Tokyo (CNN) -- The containment structure surrounding one of the reactors at a quake-battered nuclear power plant is damaged and may be leaking radioactive material, the Japanese government's point man on the crisis said Monday. The plant's owner disclosed that small amounts of plutonium had been found among contaminants around the facility late Monday as Japanese authorities struggled to explain how radioactive water was leaking into maintenance tunnels and possibly, into the Pacific Ocean. Yukio Edano, Japan's chief Cabinet secretary, told reporters Monday afternoon that "there may be a leak" from the containment vessel surrounding the No. 2 reactor. He said experts were still trying to determine the condition of the reactor's pressure vessel, which sits inside the containment vessel and immediately surrounds the radioactive fuel rods at the reactor's core. "Somehow, we understand water is being moved from one place to another," Edano said. "We need to hear an explanation from experts." Reactors 1-3 at the plant, located about 240 km (140 miles) north of Tokyo, are believed to have suffered core damage after their cooling systems were knocked out by the March 11 earthquake and tsunami that ravaged northern Japan. The tsunami knocked out backup generators that ran their coolant systems and damaged water pumps at the plant, forcing workers to scramble to prevent a meltdown. Technicians restored external electric power late Monday to the No. 3 reactor plant, a step toward restoring cooling systems there, the plant's owner reported late Monday. But hydrogen explosions -- an early symptom of core damage -- inflicted heavy damage on the buildings housing the No. 1 and No. 3 reactors in the days following the quake, and another suspected explosion rocked the No. 2 reactor on March 15. Japanese nuclear regulators and the owner, the Tokyo Electric Power Company, say they know little about what damage was sustained in that blast. No. 2's turbine house remained radioactive enough to pose an immediate hazard, authorities reported after taking new readings Monday afternoon. The 1,000 mSv/hour reading is more than 330 times the dose an average person in a developed country receives per year and can result in vomiting and up to a 30 percent higher risk of cancer, according to the International Atomic Energy Agency. The level is also four times the top dose Japan's Health Ministry has set for emergency workers struggling to control the further emission of radioactive material from the damaged plant. Cham Dallas, an expert on radiation and public health at the University of Georgia, told CNN's "American Morning" that the level suggests operators are facing "a deteriorating situation" at the No. 2 reactor. "Fortunately, that's in the reactor area, not outside and not in Tokyo or even in the area in Fukushima province," Dallas said. "But in the reactor area itself, that's -- that's concerning to me. We're starting to see levels now that are dangerous to reactor workers if they're in those contaminated areas." The officials said it was unclear how contaminated water got into the tunnel, or if it might have spilled out and seeped into the Pacific Ocean from there. "Right now, it is not known," Hidehiko Nishiyama, an official with Japan's Nuclear and Industrial Safety Agency, said Monday evening. Water was being pumped out of the No. 1 and No. 2 turbine building, but Nishiyama noted that there is no place to put water pooled in the No. 2 building's basement. The plan is to extract the water using what he called a condenser. But that apparatus is "almost full," as are several storage tanks nearby. A similar challenge is holding up the removal of collected water in the No. 3 unit's turbine building basement. "So we will first have to empty some of the tanks," he said, adding later only that the tainted water needs to be removed "as soon as possible." Seawater readings from a monitoring post 330 meters (361 yards) into the Pacific Ocean showed elevated readings of the reactor byproduct iodine-131, an isotope that loses half its radioactivity every eight days. The measurement was taken north of the discharge canal for reactors 1-4, where a reading of 1,850 times normal was recorded Sunday. And despite reduced alarms in recent days, Nishiyama noted Monday that the temperature is rising inside the No. 1 reactor -- a sign that the nuclear fuel rods in that unit remain in danger of overheating. Units 1, 2 and 3 were the only three of the six reactors operating when the magnitude 9 earthquake struck. The quake and resulting tsunami knocked out backup generators that ran their coolant systems and damaged water pumps at the plant, leaving authorities scrambling to pump water into the reactors and the spent fuel pools to prevent a meltdown.