Police have opened an attempted murder investigation after a 51-year-old woman was seriously injured when she was hit in the head by a bottle while walking through Waikiki just after midnight Saturday morning.

Police said the bottle apparently came from a nearby hotel, but they did not specify whether it had been thrown or dropped. The woman was taken to The Queen's Medical Center in serious condition.

No suspects have been identified. The case has been referred to the police department's major crimes unit as a second-degree attempted-murder case.