OKAYAMA, Japan - A powerful 7.3-magnitude earthquake jolted a wide swath of Japan's hilly southwest on Friday, injuring dozens of people, knocking boulders down hillsides and throwing groceries off supermarket shelves.
The midday quake - the country's strongest in at least five years - caught many Japanese at work, where they clutched desks as office buildings rumbled and hanging lamps swung violently.
The temblor was so strong that it was felt at a racetrack more than a hundred miles away, where drivers from around the world were practicing for the F-1 Grand Prix this weekend.
''The shaking was slight at first, and then it just got stronger and stronger,'' said Shuichi Oka, a clerk at a government office near the epicenter. ''It seemed to go on for a long time. It was a scary feeling.''
Japan's National Police said 39 people were injured in the quake, which was centered 315 miles southwest of Tokyo. None of the injuries was immediately reported to be life-threatening.
A bridge collapsed and was washed away in Okayama, also western Japan, and landslides were reported in 25 locations in the region. Nine houses were destroyed and 239 others damaged, police said.
Kyodo News service reported that 47 people were injured, and national broadcaster NHK said the toll had hit 50, but officials could not immediately confirm those numbers late Friday. Nearly 2,500 had evacuated their homes, either because of damage or in fear of aftershocks.
The damage was dramatic: Boulders rolled down a mountain and flattened the front of a car; streets buckled under the quake's force; wooden houses collapsed under the weight of their tile roofs.
The quake was followed by more than 100 aftershocks of varying intensities that continued into the night. Seismologists estimated there was a 40 percent chance of a strong quake hitting the area again by Saturday afternoon.
The light human toll of Friday's quake was a sharp contrast with the devastation that a 7.2-magnitude quake in 1995 wrought in Kobe city, where 6,425 were killed and 250,000 homes destroyed.
Had such a strong quake hit Tokyo instead of largely rural Tottori, it could have left an estimated 7,000 dead and millions homeless.
''We feel relieved because damages were not so extensive for a quake this strength,'' said Shinzaburo Nishi, a spokesman for the Central Meteorological Agency. ''It could be partly because areas near the epicenter were not densely populated.''
The city nearest to the epicenter was Yonago, an old castle town with a population of about 134,000, compared with Kobe's 1.4 million inhabitants.
At the Japanese Grand Prix in Sizuka, 155 miles east of the epicenter, the grandstand swayed for several seconds, startling visitors not accustomed to Japan's periodic quakes but causing no damage.
''It was really shaking,'' said Atsushi Suzuki, an official at the racing site. ''If you live in Japan, earthquakes aren't a big deal, but many people here were kind of freaking out.''
In Hinocho town, a small hospital shook so violently that the staff evacuated all 80 patients from the building to check it for damage.
The 28 injured in Tottori prefecture included three people who were caught in landslides and rescued by civilians and local officials. Two of the victims were trapped inside their car. The third suddenly disappeared while working at a roadside construction site.
Tsuyochi Iwashita, a spokesman for the National Police Agency, said a Shinto shrine fell apart.
The quake shut down railway lines and roads, and electricity was cut to nearly 9,300 homes and businesses, but power was restored to most of them soon afterward, police said.
Despite the strength of the quake, and many powerful aftershocks, no tsunami occurred in the Japan Sea, the meteorological agency said.
In 1943, a 7.2-magnitude quake hit eastern Tottori, killing more than 1,000 people.
