Aida Cruises says there is reason to believe that the celebrity, who first became well-known as a contestant in Germany's version of Pop Idol in 2003, jumped into the sea on Sunday morning.

"That is our suspicion," said spokesman Hansjoerg Kunze.

Aida said the ship was stopped and returned to the spot off the coast of Newfoundland where Kueblboeck was believed to have entered the water.

The 33-year-old, who tried but failed to be chosen as Germany's Eurovision entry in 2014, was travelling on the vessel in a private capacity, as one of about 2200 passengers on their way to Newfoundland from the northern German port city of Hamburg.

The incident occurred about 100 nautical miles (about 185 kilometres) north of the city of St John's on Newfoundland. The water temperature was recorded at about 10.5 degrees Celsius.

Kueblboeck's management company could not be reached for comment.

The Canadian coastguard confirmed on Sunday that it was using a surveillance plane and helicopter to search the cold Labrador Sea. Two other cruise ships also helped with the search.

Kueblboeck, born in Bavarian Hutthurm, made his last big television appearance in the eighth season of the show Let's Dance in 2015 and was studying to be an actor at the European Theatre Institute Berlin.

Australian Associated Press