At least 28 people were injured in the region and 20 residents in the town of Atsuma may be unaccounted for, officials said. Twenty of those injured were in the city of Sapporo.
The earthquake was followed by multiple aftershocks, including one registered at 5.4, public broadcaster NHK reported, 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. Officials said a main power station lost operations, affecting other sites. Independently owned power generators were assisting.
“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.
Residents said they awoke to a powerful earthquake that lasted 30 seconds to one minute.
Prime Minister Shinzo Abe said 4,000 defense forces joined rescue operations, and that number could increase to a maximum of 25,000.
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.