Philippine authorities said Thursday they had seized a huge amount of iron ore intended to be smuggled to China, as part of a long-running battle against illegal miners.

The 50,000 tonnes of iron ore, believed to be worth more than $2 million, were found stockpiled near a private wharf at a coastal mining town in the eastern province of Camarines Norte, mines bureau head Leo Jasareno said.

"A cargo ship was seen anchored at a distance, and it was believed to be waiting for the ore to be loaded when the raid happened," Jasareno told AFP.

"The shipment was supposed to go to China and they were clearly intending to smuggle it out."

Jasareno said the ore was extracted illegally because the mining companies involved did not have a mineral export permit, adding one was suspected to be a front for a Chinese firm.

Initial estimates by the bureau's experts placed the shipment's value at $50 per metric tonne, or $2.5 million, he added.

The Chamber of Mines of the Philippines last year warned of Chinese companies using Filipino fronts to take advantage of a law reserving small-scale mining for locals.

The seizure last week came four months after the government deported eight Chinese nationals caught working illegally for a mining firm. More than 100 other Chinese have been detained for similar offences over the past two years.

In 2010, a diplomatic row broke out between Manila and Beijing after police detained but eventually freed 80 Chinese found working illegally at a mine site on the main island of Luzon.

The Philippines is believed to have some of the biggest mineral reserves in the world. The government estimates the country has at least $840 billion in gold, copper, nickel, chromite, manganese, silver and iron.

But the mining industry remains relatively small because of laws that discourage investment and a very strong anti-mining lobby led partly by the influential Catholic Church.