TOKYO - Residents in western Japan were cleaning up debris Monday evening after a powerful earthquake hit the area around Osaka, the country's second-largest city, killing four people and injuring hundreds while knocking over walls and setting off fires.

The magnitude 6.1 earthquake that struck the area early Monday damaged buildings and left many homes without water or gas. The quake also grounded flights in and out of Osaka and paralyzed traffic and commuter trains most of the day.

By evening, bullet trains and some local trains had resumed operation, and stations were swollen with commuters trying to get home, many of them waiting in long lines. An exodus of commuters who chose to walk home filled sidewalks and bridges.

Some commuters took refuge in nearby shelters instead of going home. NHK public television showed dozens of men wearing ties and carrying briefcases sitting on gym mats at a junior high school gymnasium in Ibaraki city, where some families also gathered.