TOKYO (AP) — A powerful earthquake rocked Japan's northernmost main island of Hokkaido early Thursday, triggering landslides that crushed homes, knocking out power across the island, and forcing a nuclear power plant to switch to a backup generator.

The magnitude 6.7 earthquake struck southern Hokkaido at 3:08 a.m. at the depth of 40 kilometers (24 miles), Japan's Meteorological Agency said. The epicenter was east of the city of Tomakomai but the shaking also affected Hokkaido's prefectural capital of Sapporo, with a population of 1.9 million.

The Japanese national broadcaster NHK, citing its...