The quake hit at 7:49 a.m. (1049 GMT) off the coast of Hachijo, a small island about 170 miles (275 kilometers) south of Tokyo, at a depth of 25 miles (40 kilometers).
Japan is one of the world's most earthquake-prone countries, and experts believe Tokyo has a 90 percent chance of being hit by a major quake over the next 50 years.
In 1995, a magnitude-7.2 quake in the western port city of Kobe killed 6,400 people.
