A Royal Caribbean cruise ship passenger who is believed to have fallen overboard during a trip from Australia to Hawaii is still missing.

Authorities have conducted an extensive search for the man but failed to find any trace of him.

The Royal Caribbean's Quantum of the Seas, expected to dock at Honolulu on April 28, left Brisbane on April 12, CNN reported.

The ship was nearing the end of its 16-day voyage when the man reportedly fell overboard 500 miles (805 kilometers) south of Kailua Kona, Big Island.

"While on its trans-pacific sailing, a guest onboard Quantum of the Seas went overboard," the cruise company said in a statement, as per the outlet.

"The ship's crew immediately launched a search and rescue operation and is working closely with local authorities," the statement continued.

The ship stayed at the scene for a couple of hours as the search ensued for the missing passenger. Six life rings were deployed to rescue him, but no sign of the man was seen. The coast guard reportedly said the ship eventually continued on its journey to Honolulu.

A U.S. Coast Guard Hercules helicopter conducted an aerial search of the area for six hours on Wednesday. However, the search yielded no positive outcome, the coast guard said, noting that the search would resume Thursday, according to CNN.

A U.S. Coast Guard plane reportedly began scouring the area for signs of the man at around 7 a.m. local time Thursday. The search continued until the plane exhausted its fuel supply by around 3 p.m. Authorities then suspended the search for the man, news.com.au reported.

Georgina Thompson, a passenger on the ship, said she and her husband were in bed when they began hearing "Oscar, Oscar, Oscar" — the ship's code for man overboard — over the PA system Tuesday.

"There were lights, you know, the big lights shining on the ocean," Thompson told 9News. "And also there were a couple of boats out there in the water."

Thompson added that the atmosphere on the ship following the alert call and the subsequent series of events was "very somber, very somber."

Fellow passenger Susan Whittington said it was "a shocking situation to be in," according to the outlet.

Representational image (ship)
Representational image (Source: Pixabay / cocoparisienne) Pixabay / cocoparisienne