A U.S. military helicopter crashed on a university campus in southern Japan on Friday, and at least two crew members were hospitalized, police said.

The helicopter crashed at Okinawa International University, in Ginowan city on the southernmost island of Okinawa (search), Okinawa state police spokesman Takeshi Hori said.

Two crew members were taken to a hospital for treatment, Hori said. Another police official said there were a total of three injuries, but he wouldn't elaborate.

It wasn't clear how many people were on board or whether there were any civilian injuries on the ground.

Atsuhiko Kawano, a spokesman for Japan's Defense Facilities Administration Agency, said witnesses reported that the CH-53 helicopter grazed a building at the university before smashing into the ground and catching fire.

The CH-53 (search) is used by the U.S. Marines for transport of equipment and supplies, mostly for amphibious assaults.

A U.S. Forces Okinawa spokesman declined immediate comment. Phones at Okinawa International University rang unanswered.

The crash comes only days after a U.S. surveillance plane on a training mission crashed on an uninhabited island near Iwo Jima on Tuesday. Four aviators were killed.

About 50,000 U.S. military personnel are stationed in Japan under a security treaty, two-thirds of them on Okinawa, about 1,000 miles southwest of Tokyo.