A huge explosion of an oil pipeline destroyed parts of a central Mexican city Sunday, incinerating people, cars, houses and trees as gushing crude turned streets into flaming rivers. At least 28 people were killed, 13 of them children, in a disaster authorities blamed on oil thieves.

The blast in San Martin Texmelucan, estimated to have affected a three-mile radius, scorched homes and cars and left metal and pavement twisted from the intense heat.

Relatives sobbed as firefighters pulled charred bodies from the burned homes, some of the remains barely more than piles of ashes and bones.

Jose Luis Chavez, 58, who lives 10 blocks from the explosion, said he heard at least two loud booms and saw flames leap more than 30 feet. "The explosions we had were very scary," Chavez said.

In addition to the deaths, at least 52 people were hurt and 84 remained in shelters after fleeing San Martin, which is about 55 miles east of Mexico City. More than 115 homes were scorched, 32 of them destroyed.

The explosion, which happened before dawn Sunday, was apparently caused by thieves trying to steal crude oil, said Valentin Meneses, interior secretary for the state of Puebla, where San Martin is located. Investigators found a hole in the pipeline and equipment for extracting crude, said Laura Gurza, chief of the federal Civil Protection emergency response agency.

"They lost control because of the high pressure with which the fuel exits the pipeline," he said, adding that the oil began to flow down the city's streets and into a nearby river.

Several bodies were found in cars near the location of the leak, but authorities didn't know if the dead were involved in the theft or just there by coincidence.

At some point a spark caused the crude to erupt into flames, though officials didn't know the origin of the spark.

President Felipe Calderon expressed his condolences to the families of the dead and his support for those injured and affected. He said the federal government would give its full support in investigating who was responsible and bringing them to justice. No one has been arrested.

The state-owned oil company Petroleos Mexicanos, or Pemex, said in a statement that it had shut down the pipeline, and government authorities said the fire was under control by midday.

Pemex has struggled with chronic theft, losing as much as 10 percent of its product. Criminals tap remote pipelines, sometimes building pipelines of their own, to siphon off hundreds of millions of dollars worth of oil each year, Pemex has said.

In 2009, the U.S. Justice Department said U.S. refineries bought millions of dollars worth of oil stolen from Mexican government pipelines and smuggled across the border in illegal operations led by Mexican drug cartels expanding their reach.