(CNN) -- At least 28 people were killed and 52 injured after an oil pipeline exploded in central Mexico, the country's state-owned oil monopoly said.
The cause of Sunday's explosion in San Martin Texmelucan, in Puebla state, was under investigation, but preliminary reports pointed to the illegal extraction of oil from the pipe, said Laura Gurza, coordinator for civil protection in Puebla.
The situation was under control, but the extent of the damage was still being assessed, Civil Protection Director Miguel Angel Martinez said. The pipe belongs to Pemex, the state-owned oil monopoly.
Some 32 houses were lost in the blast, Martinez said. Pemex said in a statement later Sunday that a total of 115 homes were damaged by the explosion.
Video from the scene showed a huge billowing wall of smoke that reached into the sky. Rescue workers could be seen walking through the still-smoldering streets.
Thirteen of the people killed were children, the state news agency Notimex reported, citing Gurza.
About 5,000 nearby residents were evacuated, officials said, and some 200 were in a government shelter.
Oil theft has been a persistent problem for Pemex, and has been on the rise since President Felipe Calderon took office. A Washington Post investigation found that drug cartels were increasingly diversifying into other areas, including oil theft, to the tune of more than $1 billion in a two-year period.
Calderon office said the president visited the blast site Sunday to offer his support to victims and their families.
CNN en Espanol's Krupskaia Alis and Rene Hernandez contributed to this report.