Japan has issued its top tsunami warning after a major offshore quake measuring 7.9 hit today, strongly swaying buildings in Tokyo and sending people fleeing into the streets. The meteorological agency issued its top-level evacuation alerts for the entire Japanese coast, warning of a tsunami of up to six metres. The tsunami has already engulfed parts of Japan's Pacific coast and residents have been ordered to rush to high ground. It also put the territories of Guam, Taiwan, the Philippines, the Marshall Islands, Indonesia, Papua New Guinea, Nauru, Micronesia and Hawaii under a lower tsunami watch. The US Geological Survey said the quake struck about 382 kilometres north-east of Tokyo. Smoke could be seen rising from a building in Tokyo port. Police in Miyagi prefecture have reported numeorus injuries. Shinkansen bullet trains stopped when the quake struck, while the nuclear power plant in Miyagi prefecture has stopped operating. Power has been cut in Sendai city, where there are numerous reports of gas leaks. The government has set up a crisis management team at the prime minister's office.