A magnitude 6.1 earthquake shook Osaka today killing three people, halting factory lines in a key industrial area and bursting water mains, government officials and broadcaster NHK said.
Japanese media including public broadcaster NHK said collapsing walls had killed an 80-year-old man and a 9-year-old girl, and that another man in his 80s was killed after being crushed by a toppling bookcase.
At least 234 people were injured, NHK said.
The government confirmed two of the deaths. Japan does not confirm deaths until a formal examination has been made and generally uses the term cardiopulmonary arrest in such cases.
Live footage showed burst water mains and a house on fire after the quake hit Japan's second-biggest metropolis in the morning (2300 GMT Sunday) as commuters were heading to work.
Prime Minister Shinzo Abe said the government was assessing damage and that its top priority was the safety of residents.
The epicenter of the earthquake was in the northern part of the prefecture, the Japan Meteorological Agency said. The agency originally put the quake's magnitude at 5.9 but later raised it to 6.1. No tsunami warning was issued.
No irregularities were detected at the Mihama, Takahama and Ohi nuclear plants to the north of Osaka, Kansai Electric Power said.
Kansai Electric Power said no irregularities had been detected at the Mihama, Takahama and Ohi nuclear plants after the quake. Kansai also said more than 170,000 households were without power in Osaka and neighboring Hyogo prefecture.
Daihatsu Motor Co, an Osaka-based unit of Toyota Motor Corp, said it had suspended production at its factories in Osaka and Kyoto while they check for damage.
Sharp Corp said its directly owned plants in the area were operating as usual, but a joint venture plant with parent Hon Hai Precision Industry said it had halted operations for safety checks.
Honda Motor Co said production in Suzuka, was halted for checks but no problems were found and operations were back to normal.
Kate Kilpatrick, visiting Japan for the first time from the United States, said alarms went off almost immediately in the Osaka hotel she was staying and a loudspeaker told guests to stay away from windows.
"We were sleeping and it woke us up abruptly," she said.
"It was so terrifying because this is my first earthquake. I thought it was a nightmare because I was so confused. The whole world was aggressively shaking."
Osaka is to host next year's Group of 20 summit.
A massive magnitude 9.0 quake hit northeastern Japan on 11 March, 2011, triggering a huge tsunami that killed some 18,000 people and triggered the world's worst nuclear disaster in a quarter of a century at Tokyo Electric Power's Fukushima Daiichi nuclear plant.