A landslide along a long ridge in the rural town of Atsuma could be seen in aerial footage from public broadcaster NHK. At least 19 people were missing and 120 people were injured in Hokkaido after the magnitude 6.7 quake, it said.
There were no early reports of deaths but a man suffered cardiac arrest after falling down stairs, Japanese media reported.
Japan's Hokkaido Electric Power Co said it conducted an emergency shutdown of all its fossil fuel-fired power plants after the quake, leading to blackouts across Hokkaido.
Efforts to restore power to 2.95 million households were underway but it was not clear when supplies would be restored, a company spokesman said.
Japan's Trade and Industry Minister Hiroshige Seko said the ministry instructed Hokkaido Electric Power to restart the coal-fired Tomato-Atsuma power plant within a few hours.
Roof tiles and water covered floors at Hokkaido's main airport, New Chitose Airport, which would be closed for at least Thursday.
People look at an area damaged by an earthquake in Sapporo in Japan's northern island of Hokkaido, Japan.
Kansai Airport, an important hub for companies exporting semiconductors in western Japan, remained closed due to a powerful typhoon earlier this week.
Prime Minister Shinzo Abe said officials hope to reopen Kansai Airport for domestic flights on Friday.
FIRE, POWER OUTAGES
The quake, which struck at 3:08 a.m. (1808 GMT Wednesday) posed no tsunami risk, the Japan Meteorological Agency said. The U.S. Geological Survey said it struck some 68 km (42 miles) southeast of Sapporo, Hokkaido's main city.
Abe arrived at his office before 6 a.m. and told reporters his government had set up a command centre to coordinate relief and rescue. Sounding haggard, Abe said saving lives was his government's top priority.
The Tomari Nuclear Power Station suffered a power outage but was cooling its fuel rods safely with emergency power, said Chief Cabinet Secretary Yoshihide Suga. Operator Hokkaido Electric Power Co reported no radiation irregularities at the plant, which has been shut since shortly after a massive 2011 earthquake, Suga told a news conference.
A fire broke out at a Mitsubishi Steel Mfg Co plant in the city of Muroran after the quake but was mostly extinguished with no injuries, a company official said.
A row of houses could be seen slanting at odd angles, leaning against one another in one town, and many schools were closed, NHK said.
NHK footage showed a crumbled brick wall and broken glass in a home, and quoted police as saying some people were trapped in collapsed structures.
Soldiers were shown looking for damage on a rural road that was blocked by fallen trees.
A series of smaller shocks, including one with a magnitude of 5.4, followed the initial quake, the Meteorological Agency said. Agency official Toshiyuki Matsumori warned residents to take precautions for potential major aftershocks in coming days.
Shinkansen bullet trains were halted in some areas of Hokkaido, NHK said.
Japan is situated on the "Ring of Fire" arc of volcanoes and oceanic trenches that partly encircles the Pacific Basin and accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
A 9.0 magnitude earthquake, the most powerful ever recorded in Japan, struck on March 11, 2011, under the ocean off the coast of the northern city of Sendai. The quake set off a series of massive tsunami that devastated a wide swath of the Pacific coastline and killed nearly 20,000 people.
The tsunami also damaged the Fukushima Daiichi Nuclear Power Plant, leading to a series of explosions and meltdowns in the world's worst nuclear disaster for 25 years.
Saturday marked the 95th anniversary of the Great Kanto earthquake, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area. Seismologists have said another such quake could strike the city at any time.