Eight Chinese nationals will be deported from the Philippines after they were caught working illegally for a mining firm, an immigration official said Tuesday.

Their arrests last week were the third time groups of Chinese had been caught working illegally in the mining sector over the past two years, fuelling industry concerns that firms from China were pilfering the country's resources.

The eight Chinese were employed with two chromite mining firms on central Samar island, but had entered the country as tourists and had no work permits, immigration bureau intelligence chief Antonette Mangrobang told AFP.

The Department of Environment's mining director for Samar, Roger de Dios, said there were many Chinese firms in the area that were skirting a national law that banned foreign firms from small-scale mining.

"Supposedly they are Filipino companies but they are financed by Chinese nationals," he told AFP.

The Chamber of Mines of the Philippines also said there were increasing reports of Chinese companies taking advantage of the law that is meant to reserve small-scale mining for Filipinos.

"We have heard of a lot of these Chinese nationals coming in. They use these local dummies to apply for small scale mining permits and they just go on extracting minerals," said chamber vice-president Ronaldo Recidoro.

"They have no environmental safeguards. We don't know what their output is, what they do with it. Do they sell it (locally) or export it?" he said.

De Dios said some of the Chinese-linked firms on Samar illegally exported ore out of the Philippines.

"Some of them have been issued stoppage orders by the mining board. They stopped for a while, then went back to it all over again," de Dios said.

Last week's arrests came after 80 Chinese were caught working illegally at a mine on the main island of Luzon.

The immigration bureau's Mangrobang said another 26 were detained for similar offences last year on the southern island of Mindanao.

The Philippines has some of the biggest gold and other mineral deposits in the world, according to the US government, but restrictive laws and other factors make the mining industry relatively hard to access for foreign firms.

Chinese embassy spokesmen could not be contacted for comment on the latest arrests.