MASHIKI, Japan — A powerful earthquake with a preliminary magnitude of 7.1 struck southern Japan early Saturday, barely 24 hours after a smaller quake hit the same region and killed nine people.

Japanese broadcaster NHK said a number of calls were coming in from residents reporting people being trapped inside houses and buildings.

The quake shook the Kumamoto region at 1:25 a.m. Saturday. Japan's Meteorological Agency issued an advisory for a tsunami up to 1 meter (3 feet) along the coast west of the epicenter in Kumamoto. The agency said some swelling of waves had reached the coasts of Ariake and Yatsushiro, but there was no visible change in footage shown on NHK.

Sirens of patrol vehicles were heard on the background as NHK reported from the hardest-hit town of Mashiki. The asphalt ground outside the town hall had a new crack, apparently made by the latest earthquake.

Thursday's weaker, magnitude 6.5 earthquake brought down buildings and injured about 800 people, in addition to the nine deaths. The epicenter of Saturday's earthquake was about 12 kilometers (8 miles) northwest of Thursday's, and at a depth of about 10 kilometers (6 miles), Saturday's quake was more shallow.

It hit residents who were still in shock from the previous night's horrors and had suffered through more than 100 aftershocks in the interim.

Mari Yamaguchi reported from Tokyo.