(CNN) — Landslides resulting from a preliminary magnitude 6.7 earthquake early Thursday on Japan’s Hokkaido island buried a “large” number of homes at the foot of a ridge, public broadcaster NHK reported.

At least three people were injured, officials said. Rescue teams were mobilized.

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The earthquake was followed by a 5.4 aftershock, NHK said, citing the Japan Meteorological Agency. The US Geological Survey said the earthquake registered at 6.6.

Nearly 3 million households lost power, according to the Hokkaido Electric Power Company.

“The electric supply was stopped to Tomari nuclear plant, but it can operate without external electric supply for one week,” Chief Cabinet Secretary Yoshihide Suga said.

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Residents said they awoke to an earthquake that lasted 30 seconds to one minute.

Some streets were cut off by downed trees, and additional images from the broadcaster showed crumbled buildings.

Additionally, Japan Meteorological Agency officials told NHK that risks of aftershocks are substantial for as long as the next week. They warned residents about increased risks of collapse among buildings near the epicenter.

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