US and Japanese naval forces have launched a search and rescue operation after one of the American sailors was reported to have gone missing during a joint naval drill in the disputed South China Sea.

The sailor apparently fell overboard from the guided-missile destroyer USS Stethem during the exercise and was reported missing by the warship at 9am local time on Tuesday (1 August), according to defence and military news websites.

The US Navy said it would not reveal details of the missing sailor while the search is going on.

The USS Stethem, which primarily operates from Yokosuka in Japan, was on a routine mission in the hotly contested waters when the sailor's absence was noticed, a statement from the Navy's Pacific Fleet said. The destroyer is believed to have been conducting routine operations throughout the Pacific for much of this year.

On 12 July, the destroyer conducted a freedom of navigation operation in the waters and sailed within 12 nautical miles of the Paracel Islands, where China has overlapping claims with Brunei, Malaysia, the Philippines, Vietnam and Taiwan.

It added that the search operation was carried out on Wednesday too, with Japan's Maritime Self-Defence Force ships assisting the US Navy.

Helicopters from Japan's JS Izumo the US Joint Personnel Recover Center from Hawaii were also assisting, the Navy said, according to military and defence website Stars and Stripes.

The search for the Stethem sailor is reported to be the third man-overboard hunt for the US Navy since this summer.

Earlier on 8 June, the US and Japanese forces and ships spent more than 50 hours searching for Peter Mims, a Petty Officer Third Class sailor who was presumed to have gone missing from the guided-missile cruiser USS Shiloh off the coast of the Japanese island of Okinawa.

However, it was later discovered that Mims had been hiding aboard in the ship's engine room. He was reported to have purposely avoided being searched by the crew for one week. He is now reported to be facing possible discharge from the Navy, Military.com reported.

In another incident, a sailor reportedly fell from the USS Normandy off the coast of North Caroline on 6 June. Fire Controlman Second Class Christopher W Clavin was later presumed dead after the Navy abandoned the search operation after 76 hours.