MANILA - Soil and sand from two mountains "leveled" by mining in Zambales could have been used by China to build artificial islands in the South China Sea, the governor of the province said Thursday.

For three years, fishermen have reported seeing soil and sand being used by China to reclaim reefs disputed by the Philippines, as mining destroyed the mountains of Pinmagong and Binabag, Zambales Governor Amor Deloso said.

"At that time, I thought for purely mining operations of nickel... iba pala- Scarborough Shoal pala [as it turned out, it was for Scarborough]," told a Senate investigation.

Scarborough Shoal, around 230 kilometers from the Zambales coast, is a rich fishing ground that has been held by China since the end of a naval standoff in 2012.

There have been no reclamation works in Scarborough, called Panatag Shoal by Manila, but President Rodrigo Duterte claimed military intelligence reported Chinese barges were sighted in the area.

However, Carlo Arcilla, a professor at the University of the Philippines National Institute of Geological Sciences, said Deloso's suspicion was "physically impossible."

Seven million ships will be required to haul 350 billion tons of sand on soil for a 3,500-hectare reclamation, he told the same investigation.