French justice officials have concluded that pilot error caused a helicopter crash near Bordeaux in December that killed a Chinese billionaire and his son as they flew over his newly-purchased wine estate.

Christophe Auger, prosecutor of the southwest city Libourne, said an inquiry into the crash that killed 46 year-old tea magnate Lam Kok and three others had uncovered "no technical or maintenance problems."

"It was caused by human error by the pilot, and the principal reason for the accident was flying at too low an altitude," Auger told the regional paper Sud Ouest Saturday.

The fatal crash occurred December 20, 2013 during a helicopter tour of the prestigious Chateau de la Riviere estate that was to be followed by an elite tea- and wine-tasting retreat.

Kok was accompanied by his 12-year-old son, his financial advisor and the chateau's former owner James Gregoire when the helicopter crashed into the nearby Dordogne river.

The child's body was found in the submerged helicopter shortly after the accident, while the other victims were swept down river by currents and their bodies located in following weeks.

Auger noted the flight had taken off late on a winter afternoon, when darkness had nearly fallen and visibility was limited.

There had been concerns that the pilot had been drinking. Augur said that his alcohol consumption was "a contributing but not principal factor."

Kok finalised purchase of the 65 hectare estate for 30 million euros ($33 million) the day before the accident.

He was the latest Chinese investor to acquire a vineyard in Bordeaux's Fronsac wine-producing region, close to the prestigious Saint-Emilion domain.

Wealthy Chinese have developed a taste for fine French wines, and their buying power has been credited with pushing prices for certain vintages to record levels. They are also now acquiring French vineyards