A French father and son, as well as his half-brother and their guide died Monday in the French Alps after being swept away by a giant avalanche while snowboarding in the popular resort of Tignes, officials said.

The accident, at an altitude of 2,100 metres (6,900 feet), was the deadliest in the French Alps since the start of the winter and came in the middle of France's high season school-break ski holidays.

A 48-year-old man, his 15-year-old son and his son's 19-year-old half-brother -- all regulars at the resort -- were engulfed by a wall of snow and ice while exploring an off-piste area with a 59-year-old guide, rescue workers said.

The snowboarders, who had unstrapped their boards and were advancing on foot down the slope, were only a few dozen metres (yards) from a ski lift when the 400-metre-wide avalanche ripped down the mountain.

Rescuers quickly retrieved the bodies of the four, who were carrying transmitters designed to assist in the location of avalanche victims.

The search for other possible victims was called off in the afternoon after fears another teenager had joined the group proved unfounded.

"The definitive death toll is four victims," Albertville government official Nicolas Martrenchard told AFP.

Around 100 rescue workers and guides, backed by helicopters, sniffer dogs and snowploughs were deployed in the search, following initial erroneous reports that the group had numbered up to nine.

Last month, 29 people died in Italy after an avalanche buried a hotel in the central town of Rigopiano.

- 'Slab' fall -

Witnesses in Tignes, a resort near the Italian border that draws skiers from across Europe, raised the alarm at around 10:35 am (0935 GMT) after seeing the wall of snow barrel down the mountain.

The avalanche risk in the area had been listed as three on a scale of five, with five being the most serious.

At level three, a single skier can trigger a snowslide. Ski areas are closed when five is reached.

The ski resort said it was a "slab" avalanche, caused when dense wind-packed snow breaks off from a slope.

The incident brings to 14 the number of accidents recorded in the French Alps and Pyrenees so far this winter, claiming a total of seven lives.

One of the worst avalanches in the Alps in the past decade took place in the summer of 2012 in the Mont-Blanc range. Nine climbers from Britain, Germany, Spain and Switzerland were killed as they tried to scale the north face of Mont Maudit, which translates as Cursed Mountain.

Avalanches can travel at speeds of up to 400 kilometres (250 miles) per hour.

The force of the impact of last month's avalanche in Italy has been calculated by police as being equivalent to the three-storey stone and wood structure being hit by 4,000 fully loaded trucks.

burs/cb/mt