There is “genuine concern” Premier League footballer Emiliano Sala was on a light aircraft which disappeared between France and Cardiff.
It is feared the Argentine striker was one of two people on board the Piper Malibu, which went missing off Alderney in the Channel Islands on Monday night.
Cardiff City, which signed the 28-year-old from French club Nantes on Saturday, said it was “seeking clarification” as to what happened.
A search resumed at 08:00 GMT.
Guernsey police said “no trace” of the missing aircraft had been found.
It left Nantes at 19:15 and had been flying at 5,000ft when it contacted Jersey air traffic control requesting descent, the force said.
The plane lost contact while at 2,300ft.
Searches were suspended at 02:00 “due to strengthening winds, worsening sea conditions and reducing visibility”, police added.
Cardiff Airport confirmed the aircraft was due to arrive from Nantes but a spokeswoman said there were no further details.
Guernsey harbour master Captain David Barker said no distress call had been received.
He said conditions were “much better” after searches resumed.
“It’s far easier to see something on the surface in daylight,” he said. “We are looking for any traces of an aircraft, a life raft, persons in the water, life jackets.”
The Met Office said conditions were not “too intense” at the time the aircraft went missing but had become wetter and windier later in the evening.
Cardiff signed Sala for a club record £15m after protracted negotiations with Nantes.
He has been among the top scorers in France in recent years and had scored 13 league and cup goals this season, third behind Kylian Mbappe and Nicolas Pepe.
When his signing to Cardiff was announced, he said: “It gives me great pleasure and I can’t wait to start training, meet my new teammates and get down to work.”
Club chief executive Ken Choo said: “I’m sure all Cardiff City fans will join me in that and we can look forward to seeing our record signing in a Bluebirds shirt.”
The most recent tweet from Sala’s account was a picture of him and his former team-mates, captioned “La ultima ciao”, or “the last goodbye”.
— Emiliano Sala (@EmilianoSala1) January 21, 2019
Sala began his playing career at Argentinian side Club Proyecto Crecer, before moving to French club Girondins Bordeaux in 2012.
The flight disappeared off radar near the Casquets lighthouse, infamous among mariners as the site of many shipwrecks, 13km north-west of Alderney.
HM Coastguard said the disappearance was not in the UK search and rescue area, but it had sent two helicopters to help.
A spokeswoman said they were assisting Guernsey Coastguard with a search for a light aircraft off Alderney.
“HM Coastguard helicopters from Solent and Newquay have been helping to search overnight with nothing found,” she said.