Aerial views showed dozens of houses destroyed at the bottom of a hill, with a rescue helicopter winching a resident to safety.
Around three million homes lost power after the quake damaged a major thermal plant supplying the region.
The Tomari nuclear power plant in Hokkaido, which was not operational before the quake , was forced to turn to emergency back-up power to keep its cooling system working, NHK said.
Moments after the initial quake , an aftershock measuring 5.3 rocked the area and dozens more aftershocks followed throughout the night and into the morning.
Akira Fukui, from the main city of Sapporo, said: “I woke up around 3am with a vertical jolt. I put the light on but it went out shortly afterwards. All the traffic lights are out and there's no power at work.”
No tsunami warning was issued after the relatively shallow quake , which struck 62 kilometres (39 miles) southeast of the regional capital Sapporo.
“We will do our best to save lives ,” Prime Minister Shinzo Abe said after an emergency cabinet meeting.
NHK reported that nine people had lost their lives , many of them in the village of Atsuma, where the landslide engulfed the homes.
Thirty-three people were still missing, the broadcaster added.
Local media said the dead also included an 82-year-old man who fell down the stairs at his home during the quake and that around 130 people had sustained minor injuries.
Around 20,000 rescue workers, including police and members of the Self-Defence Forces were responding to the disaster, government spokesman Yoshihide Suga said. Another 20,000 SDF troops are expected to join the effort.
“I urge people in areas shaken by strong quakes to stay calm, pay attention to evacuation information... and help each other,” Suga added.
“It's going to rain (in Hokkaido). Please be very careful of further landslides ,” the spokesman warned.
Japan is still recovering from the worst typhoon to hit the country in 25 years, which struck the western part of the country on Tuesday, claiming at least 11 lives and causing major damage to the region's main airport.