A powerful earthquake tipped over barrels of nuclear waste at a power plant in northern Japan, and officials Tuesdsay were investigating whether there were any radioactive leaks as thousands of quake survivors crowded shelters. The death toll stood at nine a day after the 6.8-magnitude quake. One person was missing and another 13,000 rendered homeless, as rescue workers rushed to locate any survivors in the rubble - amid fears of landslides - and to restore severed utilities. The quake caused a leak of water with radioactive material Monday at world's largest nuclear power plant at Kashiwazaki city, near the epicenter, although officials said that leak caused no harm to the environment. On Tuesday, officials were investigating a possible second leak, saying stacked drums containing low-level nuclear waste fell at the plant during the quake and were found a day later with some of the lids open, Kyodo News agency said, citing officials in Kashiwazaki. Kensuke Takeuchi, a spokesman at the Kashiwazaki Kariwa nuclear power plant, confirmed that barrels of low-level nuclear waste had tipped over. But he could not give further details, such as whether there had been a leak. "We're currently investigating the situation and plan to deal with it as smoothly as possible," Takeuchi said, while refusing to offer further comment. Kyodo reported that about 100 drums had fallen over. Another leak at the Kashiwazaki power plant would sow further doubts about the safety of Japan's nuclear power plants, which have suffered a string of accidents and cover-ups amid deep concerns they are vulnerable in earthquakes. Monday's quake initially triggered a small fire at an electrical transformer in the sprawling plant. But it was announced only 12 hours later that the temblor also caused a leak of water containing radioactive material. Officials said the water leak was harmless and well below safety standards, but the delay in notifying the public spurred concern among anti-nuclear activists. The Kashiwazaki Kariwa nuclear plant is the world's largest in terms of power output capacity. Fifty-five reactors supply about 30 percent of Japan's electricity. Elsewhere in the quake zone, refugees packed school gymnasiums and community centers in the city, camped out on traditional Japanese futon mattresses. Fanning themselves from the muggy summer heat, they kept a wary eye on the clouds, fearing heavy rains and the landslides they could bring. Thunderstorms and flooding were expected Tuesday throughout the quake zone, increasing the likelihood that the quake-softened, water-logged ground would give way on hillsides and cause even more damage, officials said. Light rain began to fall by early afternoon in Kashiwazaki and up to 6 centimeters (2.4 inches) were expected by Wednesday morning, according to the local observatory. "The damage is more than we had imagined," Kashiwazaki Mayor Hiroshi Aida said while inspecting damaged areas of his town. "We want to restore the water supply as soon as possible so more people can return home." Nearly 13,000 people packed into evacuation centers such as schools and other secure buildings in the quake zone 260 kilometers (160 miles) northwest of Tokyo, the Fire and Disaster Management Agency said. Nine people in their 70s or 80s - six women and three men - were killed in the quake, and 19 were seriously injured. The Defense Ministry dispatched 450 soldiers to the devastated area to clear rumble, search for any survivors under collapsed buildings and provide food, water and toilet facilities. Victims formed long lines to fill bottles with fresh water. About 50,000 homes were without water and 35,000 were without gas as of Tuesday morning, local official Mitsugu Abe said. About 27,000 households were without power. Monday's water leak at the nuclear plant entailed some 1.2 cubic meters - or 1,200 liters - of water apparently spilled from a tank at one of the plant's seven reactors, and entered a pipe that flushed it into the sea, said Tokyo Electric Power Co. official Jun Oshima. Officials said there was no "significant change" in the sea water near the plant. Economy, Trade and Industry Minister Akira Amari told TEPCO on Tuesday it must not resume operations at the plant until it has made a thorough safety check. Amari also issued requests to plant operators nationwide to confirm their safety. The area was plagued by a series of aftershocks, though there were no immediate reports of additional damage or injuries from the aftershocks. The Japanese Meteorological Agency put the initial quake's magnitude at 6.8, while the U.S. Geological Survey said it was 6.6. The first quake, which hit the region at 10:13 a.m. (0113GMT) was centered off the coast of Niigata, 260 kilometers (160 miles) northwest of Tokyo. Tsunami warnings were issued, but the resulting waves were too small to cause damage.