The vessel continued to head back towards the mainland on Friday night and was scheduled to dock in Brisbane about 6am on Sunday, according to police.

Investigators were expected to meet the Pacific Dawn at the Port of Brisbane and prepare a report for the coroner, but police said late Friday that there were no suspicious circumstances.

The search has been called off for a woman fallen overboard from the Australia-based P&O; Pacific Dawn cruise ship in the Coral Sea.

A passenger overboard alert sounded on board the 245-metre, 1500-berth vessel about 4pm on Thursday, forcing the ship to double back and search through the night, about 1000 kilometres north-east of Brisbane and 300 kilometres west of New Caledonia.

But authorities suspended the search about 7.30am on Friday, acting on advice from medical experts that the woman could not have survived.

"It is with a very heavy heart that I need to let you know that we have been unable to locate our guest," the captain, speaking from the bridge, told passengers in a recording published by News Corp.

"We are still in the area of the incident and the weather conditions with the swell three to four metres, as you can see outside, the strong wind and choppy seas, made our search extremely challenging.

"And sadly, despite continuing our search through the night, We have been unable to find help.

"As a result, we have now made the extremely difficult decision to continue our journey towards Brisbane."

P&O; Cruises spokesman David Jones had earlier flagged that the search would continue until maritime authorities agreed to call it off, but admitted hopes were fading.

The ship turned around when the alert was issued and began searching in what was described by AMSA as "rough conditions with a three to four-metre swell".

Mr Jones said the ship continued in a search pattern throughout the night.

He said the search had begun immediately after a crew member reported the guest had been seen to go overboard.

"The ‘man overboard’ incident response was activated straight away," he said.

"Pacific Dawn turned around and retraced the course it was on at the time of the incident."

Passengers told News Corp the woman had gone outside to vomit and was thrown overboard when a wave hit the ship, with one saying her husband saw the whole thing. P&O; said there was nothing to support that version of events.

An Australian Maritime Safety Authority spokeswoman said expert medical advice was that the longest the woman could have survived was first light on Friday.

"The ship continued to search for a couple of hours afterwards," she said.

Both AMSA and P&O; said their thoughts and prayers were with the woman's family, which had been notified.

On Thursday, Brisbane man Damien Pesch, who was holidaying on the ship with his family, said little information had been given to passengers other than that the ship was searching for a woman.

The ship had been on a week-long cruise of Pacific islands, leaving Brisbane on Saturday.

AMSA had been liaising with New Caledonia search-and-rescue authorities and the cruise ship, with a call going out for nearby vessels to help search.

The Pacific Dawn was expected to arrive back to Brisbane later than its 6am Saturday scheduled time.

"Pacific Dawn has now resumed her course for Brisbane where preparations are being made for a late arrival on completion of the current seven-night crew to the South Pacific," Mr Jones said.

"Guests currently onboard Pacific Dawn have been advised of a likely late arrival and guests due to embark on the ship’s next cruise will be updated on boarding arrangements. "

With AAP