Hopes were fading on Monday of finding a dozen people missing after a powerful earthquake in Japan as fears of landslides hampered relief operations.

Nine people have been confirmed dead after Saturday's earthquake, which at 7.2 on the Richter scale was the most powerful to rock an inland area of the tremor-prone nation in eight years.

Twelve people were still missing including four feared buried in the rubble of the Komanoyu inn, a secluded resort with natural hot springs that was smashed to pieces by a mudslide.

Television reports said rescue workers early Monday discovered part of a body of one victim, although officials could not immediately confirm the account.

With shovels and buckets, more than 300 troops, police and firefighters resumed work at dawn sifting through the debris of the former inn.

But water was seeping from out of the landslide, turning the former pristine forest area into a swamp, local official Akira Nishimura said.

Adding to the misery, more than 300 aftershocks have been felt since Saturday in the earthquake zone, a region 350 kilometres (220 miles) north of Tokyo which was formerly not thought to lie on a faultline.

Yoko Otachime, 35, spent a second sleepless night in a makeshift shelter with her three-year-old son after their home was damaged in the quake.

"Again last night I couldn't sleep well because of the aftershocks," she said, smoking a cigarette.

"They're giving us instant noodles, miso soup and rice balls, so we're healthy, but I miss my own home," she said.

"But the worst thing here are the toilets because the water's stopped, so we have to use buckets to wash."

Dozens of people were staying in makeshift shelters. Like Otachime, most still had homes but they needed urgent repairs to restore running water.

Yukio Miura, 71, arrived at a shelter with his two granddaughters seeking supplies of water to take back to their home.

"I haven't been able to have a bath since the earthquake. We're trying not to use up the water we have. We're not washing the dishes, we just wipe things off," he said.

Japan deployed some 800 troops to the region, who plucked hundreds of people from their cut-off homes by helicopter to the main regional town of Kurihara.

After working throughout the night, troops were able to clear away debris from one major road to let residents return to their homes, said local official Katsuya Chiba.

But he said that it would still take time to open up all of the roads to the public due to fears of renewed landslides.

Rescue teams suspended the search for one construction worker after water seeped through a landslide where his two colleagues were earlier found dead, creating concerns of further instability.

Chiba said it was also difficult to find an elderly couple who were believed to have fallen off a bridge when the powerful tremor struck.

"The area is very dangerous, so we're trying to observe it by air," Chiba said.