"Sometimes you have to make it up fast, especially if you have no air in your hose if the machine stops working. It's a normal thing. It's happened to me." These are the words of 16-year-old Joseph, speaking to Human Rights Watch (HRW) last November on how he risked drowning while diving for gold in one of the many underwater deposits found in the Philippines, a practice known locally as "compressor mining."

The boy from the town of Santa Milagrosa, located some 340 kilometers (211 miles) southeast of the capital Manila, is one of the 135 people - including 65 child miners between the ages of 9 and 17 - interviewed by the human rights group over the past two years for a report on how thousands of children in the Southeast Asian country risk their lives every day in underwater gold mining.

Titled "What … if Something Went Wrong?," the 39-page document released on September 30 focuses on the hazardous conditions children face while working in illegal, small-scale gold mines, mostly financed by local businessmen, in the eastern provinces of Camarines Norte and Masbate. "Underwater mining for gold puts adult and child miners at risk of drowning, decompression sickness, and bacterial skin infections," said HRW.

The children work in unstable 25-meter (80-foot) deep pits or underwater along the coastal shore or in rivers, processing gold with mercury, a toxic metal. The rights experts explained that while diving for several hours at a time in 10-meter-deep shafts, the miners - adolescent boys and mostly adult men - receive air from a tube attached to an air compressor at the surface. But if the diesel-powered compressor stops working, miners can drown or get "the bends" coming up too quickly.

Several boys quoted in the report described moments of fear when they dived for the first time. "I was 13 the first time [I dived]. I felt scared because it's dark and deep, said 14-year-old Dennis. "Sometimes, it feels like your eardrum is going to explode. I stay underwater for one to two hours. [Once] the man above me gave me the warning that something was wrong with the compressor, so I could immediately go up. Before it [the air] runs out, I have to go up," he added.

In September 2014, a 17-year-old boy suffocated in a mine because there was no machine providing oxygen.

Beyond the fears of mine collapses and drowning, the children interviewed by the New York-based group complained of numerous health problems, including back and body pain, fevers, and spasms. "Sometimes if the machine leaks, I smell the fumes. Sometimes I feel dizzy because it’s oil," said Dennis.

The miners also work with mercury, a readily available toxic metal that is commonly used to process gold. And according to the paper, children are particularly susceptible to the metal, which attacks the central nervous system and can cause brain damage and even death.

"Unaware of the health risks, children use their bare hands to mix mercury with gold ore and create an amalgam. When they burn off the mercury to retrieve the raw gold, they breathe in toxic fumes," said Juliane Kippenberg, associate children's rights director at HRW and author of the report.

Such small-scale mines can be found in more than 30 of the 81 provinces in the Philippines, employing 200,000 to 300,000 from mostly poor, rural communities, the report said.

The Philippines is the world's 20th largest gold producer. An estimated 200,000 to 300,000 people work in the country's small-scale gold mines, according to HRW. Large and small-scale mines combined produced about 18 tons of gold in 2014, at a market value of over $700 million, according to official statistics."

The authors of the report said that while the country's central bank is the official buying agent for gold from small-scale mining, it has no process in place to check the conditions in which the gold has been mined.

The rights group says it acknowledges that the Philippine government has taken some important steps in recent years to ensure education for all, but criticizes that the number of out-of-school children in the country remains high.

"Lots of children in Masbate and Camarines Norte - mostly from impoverished households - are dropping out of school to work in gold mining," said Kippenberg.

"In order to tackle the root causes of child labor, the government needs to assist the poorest families financially and ensure their children are able to attend and stay in school," she said, stressing that while the Philippine government prohibits dangerous child labor, it has done "very little" to enforce the law.