A body has been found in a large search operation off the coast of Sydney after a man was reported missing off a cruise ship early Monday.

About 10:30am, officers from the Police Marine Area Command retrieved a body from the water. 

The alarm was raised on the P&O vessel Pacific Adventure about 4am when it was about 10 nautical miles, or 18 kilometres, off Sydney Heads.

The ship was due to dock at White Bay Terminal a few hours later but that was delayed as the search was underway.

NSW Police Marine Commander Joseph McNulty earlier said police were hopeful because one of three emergency life rings that had been deployed had not been retrieved, fuelling hope the man may have latched onto it. 

Swells of 4 to 5 metres hindered efforts of rescue teams, which searched a 60-square-nautical-mile area and used infrared technology to search for the man's heat signature. 

A second cruise ship which was in the area has also joined the search. 

Both ships tried to lower life boats in to the water but had to abort due to the rough conditions. 

Family being cared for onboard

At least three police vessels and a number of tug boats were deployed in the search, alongside the Toll rescue helicopter. 

In a statement, P&O said there were more than 2,600 guests still on board the ship, which has now been cleared to return to port in Sydney. 

"Pacific Adventure's next voyage due to depart White Bay this afternoon has been delayed, with the ship expected to leave later tonight on a four-night voyage to Queensland," it said. 

"We thank guests for their care, understanding and patience on what's been a distressing day for guests and crew.

"Our thoughts are with the family of the guest at this difficult time."

Police have launched an investigation into the death and will prepare a report for the coroner.