The Philippines has detained 18 Chinese men on suspicion of illegal black sand mining.

The Philippines' justice department raided two mine sites run by Chinese firm Hua Xia Mining and Trading Corp. in the country's northern coastal town of Aparri, detaining 18 of its employees.

The company had a permit to dredge magnetite, also known as black sand, from a nearby river but not from the coast.

Under Philippine law, it is illegal to extract any minerals within 200 metres (656 feet) of a beach.

"Nine Chinese nationals were burrowing and processing magnetite sand within the prohibited zone," Alex Lactao, the Philippines' justice department spokesman, said.

"The other nine were arrested at a nearby beach where they were building a magnetite processing plant."

The detained Chinese men lacked permits required to work in the Philippines and could face further criminal charges.

Local authorities in the Philippines say there has been a rise in the illegal extraction of magnetite, an iron ore in huge demand by China's steel mills.

80 Chinese miners were arrested from one chromite mine in in 2010 and another eight at a similar chromite operation last year.

Environmental groups say illegal magnetite mining has been stripping Philippine coasts through erosion.

They blame small-scale mining firms, most of them allegedly Chinese and often operating in collusion with local government officials.

AFP