Japan does not confirm deaths until a formal examination has been made and generally uses the term cardiopulmonary arrest in such cases. NHK said an 80-year-old man and a 9-year-old girl had been killed by collapsing walls.

Live footage showed burst water mains and a house on fire after the quake hit Japan's second-biggest metropolis just before 8 a.m. (23:00 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.

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.

"We were sleeping and it woke us up abruptly," said Kate Kilpatrick, 19, who was staying in a hotel in Osaka when the quake hit.

"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," she said.

Kilpatrick, visiting Japan for the first time from the United States, said alarms went off almost immediately in the hotel and a loudspeaker told guests to stay away from windows.

Osaka is to host next year's Group of 20 summit.

A massive magnitude 9.0 quake hit northeastern Japan on March 11, 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.

REUTERS