A powerful 7.5 magnitude earthquake has struck off northern Japan, injuring 23 people and triggering a tsunami. The quake hit late on Monday, about 80 kilometers off the coast of Aomori. Officials reported a tsunami of up to 2 feet, 4 inches centimeters in some areas. The Fire and Disaster Management Agency says people were mostly injured by falling objects. Nuclear power plants are conducting safety checks, and some train services are suspended. The Japan Meteorological Agency warned of possible aftershocks and an increased risk of a megaquake. The public broadcaster NHK said tsunami advisories were later lifted for the Pacific coastline in northern Japan.