A powerful earthquake hit wide areas on Japan's northernmost main island of Hokkaido early Thursday, triggering landslides as well as causing the loss of power at nearly all of 3 million households and a nuclear power plant to go on a backup generator.

A magnitude 6.7 earthquake struck southern Hokkaido at 3:08 a.m. Thursday (1808 GMT Wednesday) at the depth of 40 kilometers (24 miles), Japan's Meteorological Agency said.

The quake's epicenter was east of the city of Tomakomai. It also struck Hokkaido's prefectural capital of Sapporo, with a population of 1.9 million.

The U.S. Geological Survey put the magnitude at 6.6. No tsunami warning was issued.

The Fire and Disaster Management Agency said a man was found without vital signs in Tomakomai, and several people were reported missing in the nearby town of Atsuma.

Chief Cabinet Secretary Yoshihide Suga told a news conference that the authorities have received hundreds of calls about people missing and buildings collapsing. Officials are doing their utmost for the search and rescue while they assess the extent of damage, he said.

The central government set up a crisis management taskforce at the prime minister's Office, Suga said.

Three reactors at the Tomari nuclear plant were offline, but they are running on backup generators after losing external power because of the island-wide blackouts that also caused power loss at all 2.9 million households and disrupted traffic, Japan's Nuclear Regulation Authority said.

The earthquake also affected telephone service and television broadcasting in Sapporo.