Tragic details have emerged in the desperate search for an Australian man who went overboard from a cruise ship on its way to Hawaii.

The US Coast Guard was also involved in the search for the man, who was aboard the Quantum of the Seas ship that departed Brisbane for the Hawaiian islands on April 12.

Cruise operator Royal Caribbean said the guest had gone overboard on the trans-Pacific leg of the journey.

“The ship’s crew immediately launched a search and rescue operation and is working closely with local authorities,” a spokeswoman said.

The incident reportedly happened shortly before midnight on Tuesday, local time, or Wednesday night, AEST.

A caller to Sydney’s 2GB on Thursday – who gave his name only as Mark, and said he had family aboard the Quantum of the Seas – said the man who went overboard was believed to be the partner of someone who died earlier on board, following a medical emergency.

“There was a show during the night, and the music stopped before it was announced there was a medical emergency, and apparently the person passed away’,” he told the radio station.

“About 90 minutes later, the call went out that someone went overboard, and it turned out to be the partner of the person who passed away earlier.”

Cruise ship passenger Georgina Thompson, who is on board the vessel, told Nine’s Today show she heard repeated calls of a man’s name over the PA system.

“There were lights … shining on the ocean and also there were a couple of boats out there in the water,” she said.

“The light started searching along the outside of the ship.

“You just knew that something was wrong. My husband thought we might have hit something.”

Another passenger, Melbourne man Adam Glezer, who is travelling with his wife and young child, said he heard an intercom announcement of ‘Oscar’ – meaning person overboard.

“They didn’t make a big deal about it. It was mainly for staff and crew but an hour later things got more serious,” Mr Glezer told news.com.au.

“They were repeatedly calling for a fella on deck 12, who they called about four times,” he added.

“They were telling him to go to reception but repeated it four times – they then turned the ship around to look for this fella.”

Guests aboard the Quantum of the Seas had earlier commemorated Anzac Day with a dawn service.

The US Coast Guard is conducting an aerial search for the missing man.

The ship is scheduled to arrive in Honolulu on Friday.

– with AAP