Fitzgerald added that the plane "just completely vanished. There was no radio conversation."
"The plane was flying at 2000ft when it dropped off the radar so it could have flown for about five or six miles [eight to nine km] before touching down.
"But whether it was a controlled ditching or if it dived in, we just do not know. If it was a controlled ditching, you would expect to find a liferaft but if it was uncontrolled I expect an oil slick and wreckage may be found."
Britain's Coastguard received an alert at 8.23pm on Monday from air traffic control in Jersey, the largest of the Channel Islands, after it failed to make contact with the Piper PA-46 plane with two people on board, Guernsey police said. The French civil aviation authority confirmed Sala was one of people.
"The search was terminated at 2:00, with all search and rescue assets being stood down, due to strengthening winds, worsening sea conditions and reducing visibility," Guernsey police said. "So far over 1000 square miles have been searched by a total of five aircraft and two lifeboats. There has been no trace of the aircraft. The search is continuing."
Sala's last post on Instagram was a picture on Monday with Nantes players with the message: "The last goodbye".
Cardiff signed Sala for a reported £15 million ($29 million) through 2022. He was in Cardiff last week to finalise the transfer, which was awaiting international clearance.
"I can't wait to start training, meet my new teammates and get down to work," Sala said in a video posted on the club's website.
A powerful and direct player, Sala equaled his career-best total of 12 goals — achieved in the past two seasons with Nantes — in 19 league games this season. He is fifth highest scorer in the French league, one behind Paris Saint-Germain forward Neymar, who is the world's most expensive player.
"He was a polite, nice and adorable player who was loved by everybody," Nantes president Waldemar Kita told French TV channel CNews.
Nantes was due to play Entente Sannois in the French Cup on Wednesday but the third-tier club said it was postponed until Sunday "following the disappearance of the plane of former player Emiliano Sala."
Sala, who had not played for Argentina's national team, has also played in France for Bordeaux.
- AP