Rescuers clawed through dirt in a desperate search for survivors a day after a landslide buried workers in mining tunnels in a gold-rich area in the southern Philippines.

The number of people found alive rose to 15 on Saturday as some miners were recovered from a tunnel by diggers who worked through the night, said local military spokesman Lieutenant Colonel Camilo Ligayo.

The depth of collapsed earth, however, has lowered the prospect of finding more survivors, said regional civil defense chief Liza Mazo.

"We are pessimistic. It is difficult (to dig) because the landslide is 15 to 20 meters (50 to 66 feet) deep," she told AFP.

So far, only three dead bodies have been found in the rubble but officials told reporters there are at least 21 people confirmed missing after heavy rains caused the landslide in Kingking district before dawn Friday.

It is difficult to pinpoint exact numbers for the missing because of the transient nature of mining work that draws people into the area.

The landslide covered numerous illegal, small-scale gold mines on the mountainside in Kingking, including mining tunnels, houses, stores and gold processing mills.

Such illegal mining operations with inadequate safety measures, are common in the mineral-rich, but poverty-stricken southern island of Mindanao.

At the Pantukan town hall, which serves as a makeshift command centre for the disaster, more civil defense workers and soldiers departed Saturday, carrying shovels for the hour-long ride to the landslide site in Kingking.

"Time is of the essence but we are doing our best to recover the missing," said Major Jake Obligado, commander of a battalion engaged in the rescue effort.

Authorities said one person was killed and five others were injured in a landslide in the same area last month, while 21 people died when a similar landslide brought on by heavy rains hit the same place in May 2009.

The mayor of the district where the landslide occurred, Celso Sarenas said he was helpless to stop people from mining in the disaster-prone site.

"Once, I tried to have the people evacuated. But when my aide went there, they pointed a gun at him. What else can we do?" he said in a television interview.