The rains, which authorities have described as "unprecedented", cut power to more than 20,000 households in Chiba prefecture. Local authorities issued a level five emergency warning, its highest alert, on Thursday. This was downgraded to a level four by Friday morning, but they continue to warn of landslide and flooding risks. The deluge comes after a series of storms swept through Japan and neighboring countries this week, in what meteorologists forecast to be an unusually active typhoon season. Japan's Meteorological Agency said the most recent deluge was brought by warm, humid air flowing into the country's east that combined with cold air above to make atmospheric conditions extremely unstable. The rains are expected to last through late on Friday. "This case was an extremely unusual situation, even by Japan's historical weather standards”, Chiba Governor Toshihito Kumagai told reporters on Friday morning. "I have responded to many disasters in the past, but I have never experienced a case like this." Chiba, which sits right next to Tokyo, has logged more than 100mm of rain per hour since Thursday afternoon, authorities say. (BBC)