The Los Angeles class USS San Francisco ran aground while conducting submerged operations 563 kilometers (350 miles) south of the Pacific island of Guam, where it is based, a Navy statement said.

The incident occurred at 0200 GMT Saturday (12 noon in Guam), the statement said.

"The extent of the injuries and damage aboard San Francisco is still being assessed, but includes one critical injury and several other lesser injuries. The submarine is on the surface and is making best speed back to their homeport in Guam," the statement said.

"There were no reports of damage to the reactor plant, which is operating normally."

Military and Coast Guard aircraft were en route to monitor and assist in the situation, the Navy said.

Los Angeles class submarines are 109.73 meters (360 feet) long and have one nuclear reactor and one shaft, according to US Navy data.

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