The blast in San Martin Texmelucan, initally estimated to have affected 5,000 residents in a three-mile (five-kilometer) radius, scorched homes and cars and left metal and pavement twisted and in some cases burned to ash in the intense heat.

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

Officials identified all but four of the dead by Sunday night. Although they released some names, they didn't say if they were all residents of the area or possible suspects.

Housewife Zoyla Perez Cortes, 27, said she awoke about 5:30 a.m. to a strange, overpowering smell, like gasoline. Minutes later, her street looked like it was flowing in tar and then erupted in flames. Her husband knocked down a wall allowing them to escape out the back of their two-story, cement-brick home with their three children.

Her brother-in-law is being treated for burns in a hospital, but she didn't know the fate of his wife and two children.

"It was like we were living in an inferno," she said, her eyes red from crying. "Everything was covered in smoke."

Laura Gurza, chief of the federal Civil Protection emergency response agency, said that in addition to the 28 deaths, at least 52 people were hurt and 84 remained in a shelter late Sunday after fleeing San Martin,about 55 miles (90 kilometers) east of Mexico City. More than 115 homes were scorched, 32 of them destroyed.

The explosion 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, Gurza said.

"They lost control because of the high pressure with which the fuel exits the pipeline," he said.

The oil flowed more than half a mile (one kilometer) down a city street before diverting into a river. At some point a spark of unknown origin caused both to erupt in flames.

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.

Many of the buildings destroyed were humble cement homes. Gurza said people are not permitted to live near oil pipelines, but Jose Luis Chavez, 58, who lives 10 blocks from the explosion, said residents had been there for some time.

Chavez said he heard at least two loud booms and saw flames leap more than 30 feet (10 meters) in the air. It was as if a bomb had exploded underground, he added.

President Felipe Calderon arrived late Sunday afternoon to talk with displaced people in a shelter, visit the injured in a hospital and survey damage on the main street where the fuel exploded. Earlier, he expressed 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 had been detained.

Interior Minister Francisco Blake Mora mobilized several federal ministries to help victims with medical care, shelter and recovering their lost homes and property.

The state-owned oil company Petroleos Mexicanos, or Pemex, said in a statement that it had shut down the pipeline. Government authorities said the fire was under control by midday. Some areas were without electricity or water.

San Martin Texmelucan is a city of about 130,000 people, according to 2005 government figures, in view of Central Mexico's spectacular volcanos, Popocatepetl and Iztaccihuatl. Farming is important to the area's economy, along with a manufacturing sector that makes chemical and petrochemical products, pharmaceuticals, textiles and metals, the city's website says.

Pemex has struggled with chronic theft, losing as much as 10 percent of all 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.

There have been 100 such illegal taps this year all along the pipeline that exploded Sunday. It runs from Veracruz, a heavy oil producing Gulf coast state, to Mexico state outside the capital, said Juan Jose Suarez, Pemex director general.

Suarez also reported 60 illegal taps on the pipeline in the area of Sunday's disaster, and 580 nationwide this year. He said such illegal taps cause leaks in only 3 to 4 percent of the cases.

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.

Two Texas oil company officials were sentenced to probation in September for their roles in the sale of petroleum products stolen from Mexico.

Pemex sued five companies in the U.S. in June for allegedly buying stolen Mexican petroleum products.

Also in June, police arrested 13 people who they said excavated a 500-foot (150-meter) tunnel under a busy neighborhood in Mexico City to steal fuel from oil company pipelines.