WASHINGTON, Sept 29 (Reuters) - A powerful 7.9 magnitude earthquake in the Pacific off American Samoa generated a tsunami, U.S. government agencies said on Tuesday.

Sea level readings indicated a tsunami was generated in the Pacific, the Pacific Tsunami Warning Center, a branch of the U.S. National Oceanic and Atmospheric Administration, said.

The agency earlier issued a tsunami warning for New Zealand, American Samoa and other small Pacific islands.

The epicenter of the quake was located 120 miles (190 km) southwest of American Samoa, a remote Pacific island, the U.S. Geological Survey. It struck at a depth of 20.5 miles (33 km). (Reporting by Stacey Joyce, editing by Frances Kerry)