MANILA, Philippines — Most of the sailors on a U.S. Navy minesweeper that struck a coral reef in the Philippines left the ship Friday for safety reasons after initial efforts to free the vessel failed, the Navy said.

The ship ran aground Thursday while in transit through the Tubbataha National Marine Park, a coral sanctuary in the Sulu Sea, 640 kilometers (400 miles) southwest of Manila. There were no injuries or oil leaks, and Philippine authorities were trying to evaluate damage to the protected coral reef, designated by UNESCO as a World Heritage Site.

The U.S. Navy’s 7th Fleet said 72 of the 79 crew of the USS Guardian were transferred to a military support vessel by small boat. A small team of personnel will remain aboard and attempt to free the ship with minimal environmental impact, the statement said. The remaining seven sailors, including the commanding and the executive officer, will also be transferred if conditions become unsafe.