"underground coal-seam fires are the most persistent fires on Earth and can burn for thousands of years, like Burning Mountain in Australia"

"The oldest coal fire in China is in Baijigou (白芨沟, in Dawukou District of Shizuishan City, Ningxia) and is said to have been burning since the Qing Dynasty (before 1912)."

"The Centralia mine fire is a coal-seam fire that has been burning underneath the borough of Centralia, Pennsylvania, United States, since at least May 27, 1962"

"In 1979, locals became aware of the scale of the problem when a gas-station owner, then-mayor John Coddington, inserted a dipstick into one of his underground tanks to check the fuel level. When he withdrew it, it seemed hot. He lowered a thermometer into the tank on a string and was shocked to discover that the temperature of the gasoline in the tank was 172 °F"

https://en.wikipedia.org/wiki/Coal-seam_fire