The first launch over Japan in five years is part of a clear escalation by the isolated nation ahead of the Chinese Communist Party's congress later this month and U.S. midterm elections in November. South Korea's Joint Chiefs of Staff said the medium-range missile was fired at 7:23 a.m. from Mupyeong-ri in northern Chagang province and travelled about 4,500 kilometres with a maximum altitude of 970 km, the JCS said. Japan's Defense Minister Yasukazu Hamada said the missile passed over the northern Tohoku region and flew 4,600 km -- the longest horizontal distance for a projectile launched by the country. Jeffrey Lewis, a professor with expertise in East Asia nonproliferation at the U.S.-based Middlebury Institute of International Studies at Monterey, tweeted: "Based on the range, apogee and flight time, the North Korea missile was a Hwasong-12 IRBM."