Japan ? A roller coaster partly derailed at Expoland amusement park in Suita, Osaka Prefecture, killing a woman and injuring 21 people Saturday, the Osaka prefectural police said.

The second car of the Fujin-Raijin II roller coaster derailed and leaned outward, apparently causing a woman in her 20s to slam into a handrail along the track about 1 p.m., the police said.

Four men and 17 women were taken to nearby hospitals for treatment, and the park was closed down immediately after the accident. Two passengers were seriously injured, the police said.

According to the police, the passengers were left trapped on the elevated track. Rescue workers from the Suita municipal fire department rescued and treated the passengers near the site. The police suspect improper safety management may have led to the accident, and are investigating the amusement park on suspicion of professional negligence resulting in death and injury.