SEOUL -- A U.S. Navy amphibious assault ship is en route to the site where a South Korean ferry sank Wednesday morning and will be ready to offer assistance if needed, according to the U.S. Navy.

The USS Bonhomme Richard was conducting a routine patrol in the Yellow Sea when the ferry began sinking about 100 nautical miles, or 115 miles, away, according to Lt. Arlo Abrahamson, spokesman for Commander, U.S. Naval Forces Korea.

The ferry was carrying 477 people, including 325 high school students, when it sent out a distress signal shortly before 9 a.m., South Korean officials said. Almost 180 people had been rescued as of 12:11 p.m., the country's Yonhap News said.

Two MH-60 helicopters equipped with lifeboats were initially dispatched from the Bonhomme Richard to the disaster site but have since been recalled, Abrahamson said.

The ship "has established communications with the Republic of Korea on-scene commander and is standing by to assist as required," he said.

A South Korean Navy officer, speaking on condition of anonymity, said officials are waiting to see how the situation develops before requesting additional assistance from the U.S. military.

The death toll had reached two as of 1 p.m., and seven people had been reported injured, according to South Korea's National Safety Situation Center. About 290 were missing as of Wednesday afternoon, Yonhap reported.

"This is about friends helping friends, and the U.S. 7th Fleet will continue to provide assistance at the request of the ROK," Abrahamson said.

The Bonhomme Richard, based out of Fleet Activities Sasebo, Japan, had been in waters near the Korean peninsula to participate in the joint U.S.-South Korean Ssang Yong amphibious landing exercise, which ended April 7, and is scheduled to conduct maritime operations west of the peninsula from April 15-18.

"Our thoughts are with the passengers of the Korean ferry that ran aground today and their families," the U.S. Embassy in Seoul said on its Facebook page.

The cause of the sinking remains unknown.

-- Stars and Stripes’ Yoo Kyong Chang contributed to this report.