TOKYO  —  A strong earthquake shook northern Japan early Tuesday, triggering a small tsunami that struck coastal towns about 200 miles from the epicenter. There were no immediate reports of damage.

The quake, with a preliminary magnitude of 6.9, hit at 6:39 a.m. (4:39 p.m. EST Monday) and was centered off the east coast of Japan's main island of Honshu, according to the U.S. Geological Survey and Japan's Meteorological Agency.

Tsunami waves of 12 and 19 inches hit the city of Ofunato, and 4- to 12-inch waves generated by the quake struck at least four other towns in the area, the agency said. Tsunami waves are often barely noticeable in the ocean but can rise to greater heights once they reach shore.

Ross Stein, a geophysicist with the USGS in Menlo Park, Calif., said the swell amounted to "a surfable tsunami."

The quake hit at a depth of about 15 miles and was centered off the coast of Sanriku in northern Japan, 330 miles east of Tokyo, the USGS said.

Japan is one of the world's most earthquake-prone countries because it sits atop four tectonic plates. A powerful 7.2-magnitude earthquake shook northeastern Japan in August, injuring at least 59 people, triggering landslides, damaging buildings and causing widespread power outages.

There was no destructive Pacific Ocean-wide tsunami threat following Tuesday's quake, based on historical data, according to the Pacific Tsunami Warning Center in Ewa Beach, Hawaii.

However, earthquakes as large as Tuesday's can general local tsunamis capable of causing destruction along coastlines within 60 miles of the epicenter, according to the center.