An MH-60S helicopter has crashed into the sea off the coast of San Diego, California, while conducting "routine flight operations", the US Pacific Fleet confirmed on Tuesday.
One crew member of the MH-60S helicopter has been rescued, while five others are feared missing, reports said, citing the US Coast Guard.
The helicopter was aboard the aircraft carrier USS Abraham Lincoln and crashed after taking off from the ship.
No information has been provided so far concerning possible casualties.
Marine Traffic showed several US Navy warships assisting in search and rescue operations in the area.