There was little hope of finding alive Lam Kok, a 46-year-old Chinese tea-and-property tycoon, his interpreter or winemaker James Gregoire after police early Saturday recovered the body of Lam's 12-year-old son from the back of the wrecked helicopter lying in seven metres (23 feet) of water in the Dordogne river.
The four had boarded the helicopter piloted by Gregoire on Friday to make a celebratory tour of a vast Bordeaux chateau and wine-growing estate that Lam had just bought from the Frenchman.
Lam's wife had pulled out of the flight at the last minute, saying she was "scared of helicopters," said an AFP photographer who witnessed its take-off.
The doomed flight took place after a lavish event Friday marking Lam's multi-million-euro purchase of the 65-hectare (160-acre) wine estate, Chateau de la Riviere.
After searches Saturday involving police divers and sniffer dogs, authorities were Sunday to use a sonar to try and find the missing bodies.
Police reinforcements were also to add to the more than 100 officers already carrying out the search, a gendarme commander said.
Diplomats from China's embassy in France were at the scene since Saturday "to follow the search and provide assistance to the families," local French officials said in a statement.
Mangled parts of the chopper's fuselage and a camera were retrieved from the crash site, the AFP photographer saw. But police said strong currents were complicating the search for the three missing.
Lam had celebrated his purchase of the Chateau de la Riviere, one of the region's oldest estates, with an extravagant event Friday.
He held a press conference and spent time introducing himself as the new owner to staff before hosting a sumptuous meal.
Gregoire, the former owner, then offered to take Lam on a short tour of the vineyards and surrounding grounds in the helicopter.
Gregoire was seen patiently carrying out his pre-flight procedures with a checklist resting on his knees.
When the four did not return after 20 minutes, employees at the vineyard contacted emergency services.
Gregoire himself had bought the property, the largest in Bordeaux's Fronsac wine-producing region and close to the prestigious Saint-Emilion domain, in 2003 -- a year after the previous owner died in a plane crash.
During Friday's publicity event, the vineyard's managing director, Xavier Buffo, told reporters Lam's purchase was the largest Chinese investment in Bordeaux property to date.
Saturday, he expressed shock. "We can't believe this," Buffo told AFP. "We can't take it in, it's unthinkable."
The local mayor, Philippe Buisson, said it was too soon to say what Lam's wife would do with the estate.
"Right now, she is displaying courage and great responsibility," he said.
Lam and his wife headed a Hong Kong-based group named Brilliant, which specialises in rare teas and luxury hotels in China. They had plans to turn the French chateau into a high-class tea- and wine-tasting centre.
The group -- whose interests range from Pu'er, a dark fermented tea from China's Yunnan region, to top-end resorts -- also planned to build a hotel near the vineyard.
Wealthy Chinese have developed a taste for fine French wines, and their extensive buying power has been credited with pushing prices for certain vintages to record levels.
In recent years they have increasingly taken to buying French vineyards as well. The value of each transaction has generally been under 10 million euros
($13.6 million), but Lam's purchase was estimated at much more than that.