At least 17 people have died and up to 1,000 have been injured in a series of earthquakes and aftershocks which shook northern Japan for 12 hours.
Houses were damaged in the town of Ojiya
The first quake measured 6.8 and was centred in Niigata state, 260km (160 miles) north of Tokyo.
It caused landslides and blackouts, cut water and telephone services and left almost 300,000 people without power.
Some houses have been destroyed by the tremors, roads were torn open and a bullet train was derailed.
An elderly man and woman and a two-month-old baby apparently died from the shock of the jolts in the Niigata area.
Three other children died after being buried under collapsed buildings.
Two people including a 55-year-old man died after being hit by falling concrete blocks in the town of Ojiya, in Niigata state.
Another man, in his 30s, was killed as a wall collapsed in Tokamachi, near Ojiya.
Kana Miyagawa, 20, said her world turned black when the quake hit. She recalled struggling from beneath furniture that had toppled on top of her.
"I couldn't move, I couldn't breathe, she said.
She eventually got out and ran into the street, before remembering her grandmother and turning back to find her in a kitchen strewn with broken crockery and upended furniture.
Some 61,000 people were evacuated to emergency shelters, while others spent the night in cars.
Rescue efforts were hampered by darkness and buckled roads.
The first quake struck at 1756 local time (0856 GMT). Intermittent aftershocks included a 5.9 quake which hit 16 minutes later.
Japanese television said a number of people had been injured by objects falling from shelves.
A high-speed bullet train on the Tokyo-Niigata line jumped the tracks during the first quake, while it was travelling near the epicentre.
But train operator JR East Japan said there were no injuries.
"The train has not overturned but it is tilting," a JR official said.
It was reported to be the first derailment of a bullet train carrying passengers since they were introduced 40 years ago.
Tunnels cave in
Cracks in the roads appeared near the epicentre with motorists reporting seeing the road "rise up in front of them", a BBC correspondent said.
Two tunnels also collapsed along the Tokyo-Niigata highway.
Sewage and water mains burst, and gas and telephone services were put out of action. Around 280,000 homes were without electricity.
People in some parts of Niigata had difficulty standing during the quakes.
Prime Minister Junichiro Koizumi told his ministers to make their "utmost efforts to rescue victims and collect information related to the earthquake", a news report said.
The defence agency has set up an emergency office and sent 11 military aircraft to monitor the hit region from the sky.
A magnitude six quake can cause heavy damage to buildings, and send furniture toppling over.
The quake comes days after Japan was hit by its deadliest typhoon for a decade, which killed more than 80 people.