Against the same extraordinary setting that brings Western visitors - of whom there are increasing numbers, now that Vietnam has embraced doi moi (innovation and change) - local miners work in a 1.5sq km open-cast pit. Many of the workers are women, though they are barred from the most dangerous jobs. There are a few ancient pieces of Chinese or Russian heavy machinery, but after the coal has been blasted from the seam most of the work is done by hand: huge lumps are broken into manageable pieces with hammers, then carried in baskets for grading before being taken to barges moored in the bay.
The French colonial administration began mining the area in the 1930s, and more than half a century's production has buried the beach 6ft deep in slag. Even this, though, supplies a living for hundreds of families, who comb the black mounds and sift the shallows for waste coal. ("They are fishing," an embarrassed guide told one foreigner who asked what they were doing.) Children as young as three help to gather the precious lumps into baskets, which sell to middlemen for about 15p a load.
The underground mines are scarcely less primitive. Accidents are common - a methane gas explosion killed 16 workers in January - and the damp conditions breed parasitic hookworms. Dust and sulphur fumes cause respiratory ailments; skeletal problems are common in the cramped galleries. But the 25,000 workers in the coalfields of Cam Pha, which produce 12 million tons of anthracite a year, are envied by most Vietnamese. Their wages, starting at about pounds 36 a month, are double the national average and almost five times the official salary of a hospital doctor. Miners can afford to buy a small home, a motorcycle, a colour television - all the things that people emerging from a subsistence economy aspire to.
All thanks to doi moi? It's not quite that simple. Vietnam remains a Communist country, run by cadres with a sketchy grasp of market economics and little instinct for public consultation. Particularly in the north, which has been Communist since the French were driven out in the 1950s, reform has often been half-hearted and imperfectly applied. When the leadership decided in the late 1980s to emulate the market-orientated economics introduced in China, the message for some officials, schooled all their lives to regard capitalism as a form of legalised thievery, was that they should help themselves to state assets and use them to get rich.
Vietnam's semi-transformed economy was already suffering when the Asian downturn began two years ago, and will take longer to recover than those of neighbouring countries. From the point of view of the foreign tourist, this may seem a blessing: decades of stagnation meant that much of the country's charm had been preserved, though private enterprise and the influx of foreign investment were beginning to have their effect. In Hanoi, for example, the Old Quarter is full of 1,000-year-old "tube houses". This unique form of architecture dates from the days of the emperors, when each merchant was allocated a narrow street frontage: since the only way to expand was backwards, houses that were 10ft wide were sometimes more than 100ft deep. In recent years, though, many have been illegally demolished; in some cases new buildings, still only 10ft wide, have been erected to a height of six storeys. With their white cornices and balustrades, they resemble slices of wedding cake.
In Ha Long, too, modernisation may mean the destruction of the very thing the tourists come to see. High-rise hotels would ruin the natural beauty of the bay, but that can hardly be expected to matter to the local miners. Implementation of doi moi in the coalfields has been typically haphazard. In 1988 piece rates were introduced, encouraging workers to increase production. At the same time, private companies were allowed to take over some of the smaller mines. Both changes had the effect of increasing unemployment, as enterprises began to be run for a profit rather than as a disguised form of social welfare. Some miners subcontracted their work, taking a percentage of the money earned. In 1996 the state banned private mines again. Since then, say workers, wages have fallen by a fifth.
Conditions are unlikely to improve when there is no outlet for public grievances, far less the right to strike. But at least the miners are still in work. When photographer Barry Lewis returned from Vietnam, he went to stay in a cottage in the Brecon Beacons, not far from the closed pits of south Wales. The cottage had an open fire, fuelled by coal from Cam Pha.