Catholic priest Sammy Rosimo followed truck tread marks to a coastal mine in the northern Philippines, where a stockpile of fine black sand presided over scenes of a desert apocalypse.

Instead of tall, brush-covered sand dunes that have for centuries protected the small farming town of Caoayan from the powerful waters of the South China Sea, trenches cut through barren beaches.

"This is the death sentence of the people of Caoayan," said Rosimo, a local priest, as he accompanied AFP to the recently abandoned mine.

"The dunes are the natural barrier to the salt water, like a sea wall. Without them the sea floods inland at high tide."

As with many other beaches in the Southeast Asian archipelago, Caoayan's coast has been stripped in recent years for its magnetite, an iron ore that is in huge demand by China's steel mills.

Environment groups, national authorities and the nation's big miners all blame small-scale mining firms, most of them allegedly Chinese and often operating in collusion with shady local government officials, for the devastation.

"They're giving the industry a bad image," Ronald Recidoro, vice president of the country's Chamber of Mines, which groups 35 large miners, told AFP.

Clemente Bautista, national coordinator of Kalikasan, a coalition of environment groups, said the problem was particularly acute in four northern provinces, where dozens of beaches were in retreat and river banks crumbling.

"There was a school that was swallowed up by the sea water because of black-sand mining," Bautista said.

When AFP toured the area, the coast at San Vicente town near Caoayan had retreated inland by several metres (yards) from where the sand had been scooped up.

While the ocean has yet to spill into San Vicente or Caoayan, locals believe it is only a matter of time.

"We fear being swept out to sea. We asked our local officials to stop the mining, but they ignored us," a white-haired elderly woman from Caoayan told AFP.

The woman declined to give her name, saying she was wary of openly antagonising local officials whom she accused of conniving with the miners.

The mine at Caoayan was shut in January by the national government's Mines and Geosciences Bureau, part of the environment ministry, for breaching a law against mining close to the ocean.

The firm's earthmovers, trucks and conveyor belts lay abandoned nearby. Officials from the company, which the bureau and provincial officials said was Chinese, could not be contacted for comment.

Carlos Tayag, regional chief of the mines bureau, said black-sand miners regularly flouted a law that banned all forms of mineral extraction inside 200 metres (656 feet) of the water's edge at low tide.

"The main impact is coastal erosion," Tayag told AFP.

Under the country's mining law, the environment ministry has regulatory oversight over big operations but not small-scale miners, who are defined as using only light equipment and no explosives.

Instead small-scale miners are licensed by local governments, which often lack the expertise or will to properly supervise them.

Bautista said corruption was a problem, with mining firms widely suspected of bribing local officials or offering to share profits with them to win licenses.

"Given the strong opposition of local communities against magnetite mining, the continuing operations of these Chinese (firms) in these provinces were likely made possible with the collusion of corrupt local government officials," Bautista said.

Tayag said the national government was able to step in and start closing some of the black-sand mining operations, such as the one at Caoayan, because it had breached the law banning extraction close to the water.

Tayag said most of the output from the operations was being shipped to China.

Recidoro, from the Chamber of Mines, said large miners were furious at the black-sand mining, which he said was being mainly done by Chinese firms and in many provinces across the country.

"You're disturbing the ecosystem there, and there should be a remediation process in place before you're allowed to do it," he said.

"For big mines like our members that would involve putting up anti-siltation measures, making sure whatever flora or fauna is found there is identified and protected, and the displaced native species must be replaced with the same native species."

Recidoro said the Chinese firms typically used Filipino front companies to secure mining permits from local officials.

Bautista said that while magnetite was the main mineral being mined on the coasts, Chinese entities were also involved in extraction of gold and nickel inland in some areas including Zambales province, near Manila.

Reports of Chinese nationals being caught for flouting mining laws have occurred frequently in recent years.

Authorities arrested 80 Chinese miners from one chromite mine in Zambales in 2010, and another eight at a similar chromite operation in the central island of Samar last year.

Luis Singson, interviewed by AFP shortly before his three-year term as governor of Ilocos Sur province ended last month, confirmed to AFP that he authorised several Chinese firms to mine for magnetite in Caoayan and San Vicente.

But he said residents had supported these projects, and the firms built village roads and school buildings as payback for the host communities.

"Why should I stop progress in those villages?" Singson said.

Singson also insisted mining magnetite was good for the environment, saying the black sand had washed down from the mountains "millions of years ago" and prevented vegetation or crops from growing along the coast.

"Black sand is not natural in those areas... it should be removed," he said.