It's not completely clear how the fire started, but most historical accounts hold that burning trash in a landfill near an abandoned strip mine ignited an exposed coal vein. The fire spread throughout a labyrinth of coal mines beneath the town, creating a giant underground inferno.

That was 50 years ago on May 27, 1962.

Half a century later, Centralia, Pennsylvania still burns.

The once bustling coal-mining town — then home to over 2,000 people — is now a smoldering expanse of overgrown streets, cracked pavement and charred trees. Everywhere, streams of toxic gas spew into the air from hundreds of fissures in the ground.

Workers battled the fire for almost two decades, but all attempts to extinguish the massive blaze proved unsuccessful.

In 1981, amid growing health concerns over dangerous levels of carbon monoxide, Centralia's plight was launched onto the national radar when a 12-year-old boy fell into a sinkhole. Decades of intense underground heat was causing the pavement to crumble.

In the following years, Congress set aside more than $42 million to relocate residents. Abandoned houses were bulldozed to the ground. Some townspeople, however, refused to leave.

In 2010, the town's last nine residents were fighting to keep the state from evicting them and demolishing their homes.

Experts say there is enough coal to fuel the fire for another 250 years.