Johannesburg - Tunnels coursing through the bowels of the earth under the city of Johannesburg contain precious treasure - copper cables that are being stripped out and smuggled as far away as Asia.
As in many other parts of the world, copper cable theft is not new in South Africa, but lately it has reached an unprecedented scale.
A recent brazen theft knocked out power and plunged the central business district of Johannesburg, the economic hub, into darkness, largely paralysing business for 10 straight days.
It is estimated that nearly half of the power outages in the city are caused by cable theft.
"In 2004, about four percent of all outages were due to cable theft, and now it is 40 (percent)," said Louis Pieterse, a director of the City Power utility company.
Last month's raid saw 32km of cables being ripped out, stolen or damaged, leaving the city with a R45 000 000 bill in repairs.
The damage was so severe that it took two-and-half days before technicians could safely navigate down the hot and smoky underground tunnels.
The burglary tactics are shockingly dangerous. Thieves set fire to a portion of the cables, triggering a short circuit which trips the power and allows them to tear the rest down and cart it away.
Cables thieves work for "sophisticated gangs" and "mafias", according to metal expert Rens Bindeman.
They have organised themselves into networks of metal spotters, cutters, transporters and even run an informal "training centre" near Johannesburg.
While stolen copper was traditionally sold to scrap metal dealers for recycling, now the gangs also operate from remote farms, equipped with copper-melting plants.
The cables are melted into ingots before they are shipped for export, making it virtually impossible for authorities to differentiate them from legitimately mined and processed copper.
"There is a new trend. They are getting sophisticated. They melt it into ingots," said Bindeman.
It appears that the ebb and flow in copper cable heists are tied to the international commodity prices.
Official market prices surged 60% in the last 18 months to reach almost $7 000 a ton.
The stolen copper is usually trafficked to China and India for manufacturing electronic components.
In Johannesburg, a small tunnel still reeks of burnt copper as electricians in gloves and rubber boots struggle to unfurl new rolls of cabling and restore power.
To clamp down on the pervasive thefts, city authorities plan to seal the manholes leading to the tunnels and install smoke detectors - at a cost of five million rand.
Eventually, the city also plans to replace copper with less valuable aluminium.
"The criminals who steal our copper cable sabotage our economy," said Johannesburg mayor, Herman Mashaba.
Businesses had no choice but to hire generators.
"It is catastrophic," said laundromat owner Godfrey Gonese, who lost a third of his month revenue due to the 10-day blackout.
A nearby internet cafe had to double fees to make up for the cost of running the generator and the result was "most of our customers have run away," said owner Bright Assim.
A R100 000 bounty for anyone with information about the copper burglars quickly yielded results.
In just two days, 22 people had been arrested - among them foreign nationals from India and Cameroon.
To try to stop the thefts, Johannesburg metro police in September created a specialised copper crime-busting unit.
But the war against copper theft is being short-circuited by corruption.
In a suspected bribery case captured on video and released on social media recently, policemen were seen receiving cash and driving off from a metal scrap yard.
"We suspect that officials in the city are involved, contractors as well, because they have maps of the tunnels running underneath the city, and police also," said Lucky Sindane, spokesman of the police forensic and investigation unit.