The Navy's 7th Fleet said in a statement that the crew of the USS Guardian was working to find out the best method of safely extracting the ship. Winds and waves were stronger Friday and may make it more difficult to free the ship, Philippine officials said.
It had just completed a port call in Subic Bay, a former American naval base west of the Philippine capital, when it hit the reef Thursday in the Tubbataha National Marine Park, a World Heritage Site in the Sulu Sea, 640 kilometers (400 miles) southwest of Manila.
The ship was not listing or leaking oil but its bow struck the reef, said Angelique Songco, head of the government's Protected Area Management Board, after flying over the ship in a Philippine Air Force plane. "(The ship) does not appear to be damaged."
She said it was unclear how much of the reef was damaged. She said the government imposes a fine of about $300 per square meter (yard) of damaged coral.
In 2005, the environmental group Greenpeace was fined almost $7,000 after its flagship struck a reef in the same area.
The World Wide Fund for Nature Philippines said in a statement that according to an initial ocular inspection, the 68-meter (74-yard) long, 1,300-ton Guardian damaged at least 10 meters (yards) of the reef.
Songco said that park rangers were not allowed to board the ship for inspection and were told to contact the U.S. Embassy in Manila. Their radio calls to the ship were ignored, she said.
The Tubbataha Reef is one of the most biologically diverse areas in the Coral Triangle, the world's cradle of marine life. It is off-limits to fishing and the collection of corals, wildlife and any marine life is prohibited. In 1992, UNESCO designated the reef as a World Heritage Site.
U.S. Navy ships have stepped up visits to Philippine ports for refueling, rest and recreation, and joint military exercises as a result of a redeployment of U.S. forces in the Asia-Pacific region. The Philippines, a U.S. defense treaty ally, has been entangled in a territorial dispute with China in the South China Sea.