A sailor was reported missing from a US Navy destroyer in the South China Sea early on Tuesday.

The sailor could not be accounted for on the guided-missile destroyer USS Stethem at about 9 a.m. local time Tuesday, according to a statement from the US Navy’s Pacific Fleet.

According to an official, the missing sailor had checked in aboard the ship shortly before his disappearance. A Navy official told AP the sailor is a male lieutenant, but his name is being withheld as the search continues.

A search and rescue operation is underway, with the assistance of the Japan Maritime Self-Defense Force destroyer Sazanami and helicopter carrier Izumo, said the US Pacific Fleet.