A Canadian photographer has won what is said to be the world's richest photographic prize, the Prix Pictet.
Benoit Aquin travelled to northern China to record an ecological disaster which is turning 400,000 square km of once-fertile farmland into desert.
The Prix Pictet - sponsored by a private Swiss bank - is worth 100,000 Swiss francs (£50,000; $90,000) and aims to foster environmental awareness.
It was presented in Paris by former UN Secretary General Kofi Annan.
For the inaugural prize, awarded by Swiss bank Pictet et Cie, photographers were invited to submit pictures on the theme of water - though in fact the winner, Mr Aquin, took the absence of water as his subject.
His pictures show people struggling in arid streets and landscapes against the dust storms which blow almost constantly in the affected area.
Mr Aquin's photos are on show, with those of the other 17 photographers shortlisted from among almost 250 entries, in Paris at the Palais de Tokyo.
Dust and desolation
In one of Mr Aquin's photographs, two women, smartly dressed but swathed in scarves and sunglasses against the dust, stride across a street of ramshackle houses in Inner Mongolia.
Another shows a street in the town of Hongsibao in Ningxia Province, now overwhelmed by "ecological refugees" from the surrounding countryside whose livelihoods have disappeared.
A third shows a farmer standing in the cracked and dried out bed of what used to be a pond.
The crisis has been caused by over-grazing and by pumping too much water for irrigation from underground aquifers, which are now running dry.
The parched soil is blown away by the wind and creates dust storms which reach as far as Beijing, Korea, Japan and even North America.
Mr Aquin told the BBC he has made several visits to the region, and hopes to return.
The dust makes photography difficult - and in an age before digital cameras it would have made changing film well-nigh impossible.
Mr Aquin says his personal favourite among his pictures is an especially desolate shot of a motorcyclist, her face invisible beneath her scarves, riding along a road lined by sand-coloured poplars and through a cloud of thick smoke from a burning truck beside the road.
The chairman of the Prix Pictet judges, Frances Hodgson, head of the photographs department at Sotheby's, said the aim of the prize was to persuade decision-makers in business, politics and non-governmental organisations to take notice and to act.
The exhibition will later tour to other cities around the world, starting with Dubai, where it will coincide with a meeting of the World Economic Forum.
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