TOKYO (AP) – A powerful earthquake with a preliminary magnitude of 7.1 struck Japan’s northern island of Hokkaido early Monday, swaying buildings, throwing objects off shelves and triggering a tiny tsunami wave that reached the shore.

Eight people were injured by the 3:32 a.m. quake, but there were no immediate reports of damage.

Japan’s Meteorological Agency quickly issued a tsunami warning for the eastern shores of Hokkaido’s Pacific coastal area. Tsunami are potentially dangerous waves triggered by seismic activity.

But agency official Masahiro Yamamoto later told a televised news conference that the agency had lifted its warning, saying it had detected a 4-inch tsunami and expected only small changes in the ocean’s surface.

The quake was centered off Hokkaido’s east coast, about 550 miles northwest of Tokyo, 30 miles below the sea surface.

The rocking was felt throughout northern Japan, including Hokkaido’s largest city, Sapporo, and Kushiro, on the island’s eastern shore.

The initial tremor was followed by a 4.6-magnitude aftershock about a half hour later.

National broadcaster NHK showed footage of desks rumbling in their offices and convenience store goods thrown from shelves by the force of the quake.

Among the injured were several elderly Japanese, including an 80-year-old man who broke rib bones after being thrown down by the shaking, NHK reported. The others injuries weren’t serious, NHK said.

Hundreds of homes temporarily lost power and natural gas services, NHK reported.

A magnitude 7 earthquake can cause widespread, heavy damage.

AP-ES-11-28-04 1602EST