SUBIC BAY, the Philippines — Marines from the Philippines and the United States began 10 days of joint exercises focused on disaster relief, humanitarian assistance and maritime security.

The exercises, now in their 29th year, come at a time of increased tensions in the South China Sea with the Philippines and China involved in a territorial dispute over islands lying near rich energy deposits.

About 2,600 American Marines and 1,200 of their Philippine counterparts will be training around the northern island of Luzon.

“Today, we stand side by side as we face common threats,” said Brig. Gen. Craig Q. Timberlake of the United States Marines at the opening ceremony, held on the American amphibious assault ship Bonhomme Richard in Subic Bay, a former United States naval base in the Philippines that is now a commercial port. On the assault ship’s deck, ground-attack Harrier jets were lined up near CH-46 Sea Knight helicopters. At the pier next to the ship was the Olympia, a nuclear-powered fast-attack submarine.