SAN DIEGO -- Helicopter crews from a San Diego-based ship and Marines from Camp Pendleton Thursday joined a flood relief effort in monsoon-struck Pakistan.

Nineteen cargo-carrying helicopters are aboard the amphibious assault ship Peleliu and other ships in a strike group in international waters off Pakistan, according to the Pentagon.

Marines from the 15th Marine Expeditionary Unit are aboard the same ships.

The Navy and Marine Corps helicopter crews will relieve a half-dozen Army helicopter crews that have been bringing supplies to flood-stricken areas.

The Peleliu strike group and the 15th Marine Expeditionary Unit were already on a training mission in the Western Pacific, according to the Pentagon.

Defense Secretary Robert M. Gates announced Wednesday the Peleliu is off Pakistan's port city of Karachi and will provide airlift assistance.

Gates also said the USS Kearsarge -- another helicopter landing ship -- is headed to Pakistan to relieve the Peleliu.

"Pakistan is our friend and ally, and in their time of need, we're committed to partnering with their government and military," Marine Gen. James Mattis, commander of the U.S. Central Command, said in a U.S. Central Command statement.

Despite bad weather, six helicopter crews in partnership with Pakistani military have rescued more than 3,000 people and transported more than 300,000 pounds of relief supplies to flooded areas of Pakistan since Aug. 5, according to U.S. Central Command.